[DOCS] Use a better name for fields in examples to avoid ambiguity

Previously, this doc was using a field called "content". This is
confusing, especially when the doc starts talking about the content of
the content field.  This change makes the field name "comment" which
is less ambiguous and also changes some related field names in the doc
to make a consistent example theme of editing docs around blog posts.

docs/reference/search/request/highlighting.asciidoc

@@ -15,14 +15,14 @@ GET /_search
     },
     "highlight" : {
         "fields" : {
-            "content" : {}
+            "comment" : {}
         }
     }
 }
 --------------------------------------------------
 // CONSOLE
 
-In the above case, the `content` field will be highlighted for each
+In the above case, the `comment` field will be highlighted for each
 search hit (there will be another element in each search hit, called
 `highlight`, which includes the highlighted fields and the highlighted
 fragments).
@@ -71,14 +71,14 @@ natural languages, not as well with fields containing for instance html markup
 * Treats the document as the whole corpus, and scores individual sentences as
 if they were documents in this corpus, using the  BM25 algorithm
 
-Here is an example of setting the `content` field in the index mapping to allow for
+Here is an example of setting the `comment` field in the index mapping to allow for
 highlighting using the postings highlighter on it:
 
 [source,js]
 --------------------------------------------------
 {
     "type_name" : {
-        "content" : {"index_options" : "offsets"}
+        "comment" : {"index_options" : "offsets"}
     }
 }
 --------------------------------------------------
@@ -113,7 +113,7 @@ will be used instead of the plain highlighter.  The fast vector highlighter:
   for things like phrase matches being sorted above term matches when
   highlighting a Boosting Query that boosts phrase matches over term matches
 
-Here is an example of setting the `content` field to allow for
+Here is an example of setting the `comment` field to allow for
 highlighting using the fast vector highlighter on it (this will cause
 the index to be bigger):
 
@@ -121,7 +121,7 @@ the index to be bigger):
 --------------------------------------------------
 {
     "type_name" : {
-        "content" : {"term_vector" : "with_positions_offsets"}
+        "comment" : {"term_vector" : "with_positions_offsets"}
     }
 }
 --------------------------------------------------
@@ -142,7 +142,7 @@ GET /_search
     },
     "highlight" : {
         "fields" : {
-            "content" : {"type" : "plain"}
+            "comment" : {"type" : "plain"}
         }
     }
 }
@@ -163,7 +163,7 @@ GET /_search
     },
     "highlight" : {
         "fields" : {
-            "content" : {"force_source" : true}
+            "comment" : {"force_source" : true}
         }
     }
 }
@@ -241,7 +241,7 @@ GET /_search
     "highlight" : {
         "tags_schema" : "styled",
         "fields" : {
-            "content" : {}
+            "comment" : {}
         }
     }
 }
@@ -271,7 +271,7 @@ GET /_search
     },
     "highlight" : {
         "fields" : {
-            "content" : {"fragment_size" : 150, "number_of_fragments" : 3}
+            "comment" : {"fragment_size" : 150, "number_of_fragments" : 3}
         }
     }
 }
@@ -294,7 +294,7 @@ GET /_search
     "highlight" : {
         "order" : "score",
         "fields" : {
-            "content" : {"fragment_size" : 150, "number_of_fragments" : 3}
+            "comment" : {"fragment_size" : 150, "number_of_fragments" : 3}
         }
     }
 }
@@ -317,7 +317,7 @@ GET /_search
     "highlight" : {
         "fields" : {
             "_all" : {},
-            "bio.title" : {"number_of_fragments" : 0}
+            "blog.title" : {"number_of_fragments" : 0}
         }
     }
 }
@@ -345,7 +345,7 @@ GET /_search
     },
     "highlight" : {
         "fields" : {
-            "content" : {
+            "comment" : {
                 "fragment_size" : 150,
                 "number_of_fragments" : 3,
                 "no_match_size": 150
@@ -375,7 +375,7 @@ GET /_search
     "stored_fields": [ "_id" ],
     "query" : {
         "match": {
-            "content": {
+            "comment": {
                 "query": "foo bar"
             }
         }
@@ -385,7 +385,7 @@ GET /_search
         "query": {
             "rescore_query" : {
                 "match_phrase": {
-                    "content": {
+                    "comment": {
                         "query": "foo bar",
                         "slop": 1
                     }
@@ -397,21 +397,21 @@ GET /_search
     "highlight" : {
         "order" : "score",
         "fields" : {
-            "content" : {
+            "comment" : {
                 "fragment_size" : 150,
                 "number_of_fragments" : 3,
                 "highlight_query": {
                     "bool": {
                         "must": {
                             "match": {
-                                "content": {
+                                "comment": {
                                     "query": "foo bar"
                                 }
                             }
                         },
                         "should": {
                             "match_phrase": {
-                                "content": {
+                                "comment": {
                                     "query": "foo bar",
                                     "slop": 1,
                                     "boost": 10.0
@@ -452,9 +452,9 @@ GET /_search
         "fragment_size" : 150,
         "fields" : {
             "_all" : { "pre_tags" : ["<em>"], "post_tags" : ["</em>"] },
-            "bio.title" : { "number_of_fragments" : 0 },
-            "bio.author" : { "number_of_fragments" : 0 },
-            "bio.content" : { "number_of_fragments" : 5, "order" : "score" }
+            "blog.title" : { "number_of_fragments" : 0 },
+            "blog.author" : { "number_of_fragments" : 0 },
+            "blog.comment" : { "number_of_fragments" : 5, "order" : "score" }
         }
     }
 }
@@ -508,8 +508,8 @@ ways.  All `matched_fields` must have `term_vector` set to
 combined is loaded so only that field would benefit from having
 `store` set to `yes`.
 
-In the following examples `content` is analyzed by the `english`
-analyzer and `content.plain` is analyzed by the `standard` analyzer.
+In the following examples `comment` is analyzed by the `english`
+analyzer and `comment.plain` is analyzed by the `standard` analyzer.
 
 [source,js]
 --------------------------------------------------
@@ -517,15 +517,15 @@ GET /_search
 {
     "query": {
         "query_string": {
-            "query": "content.plain:running scissors",
-            "fields": ["content"]
+            "query": "comment.plain:running scissors",
+            "fields": ["comment"]
         }
     },
     "highlight": {
         "order": "score",
         "fields": {
-            "content": {
-                "matched_fields": ["content", "content.plain"],
+            "comment": {
+                "matched_fields": ["comment", "comment.plain"],
                 "type" : "fvh"
             }
         }
@@ -546,14 +546,14 @@ GET /_search
     "query": {
         "query_string": {
             "query": "running scissors",
-            "fields": ["content", "content.plain^10"]
+            "fields": ["comment", "comment.plain^10"]
         }
     },
     "highlight": {
         "order": "score",
         "fields": {
-            "content": {
-                "matched_fields": ["content", "content.plain"],
+            "comment": {
+                "matched_fields": ["comment", "comment.plain"],
                 "type" : "fvh"
             }
         }
@@ -572,14 +572,14 @@ GET /_search
     "query": {
         "query_string": {
             "query": "running scissors",
-            "fields": ["content", "content.plain^10"]
+            "fields": ["comment", "comment.plain^10"]
         }
     },
     "highlight": {
         "order": "score",
         "fields": {
-            "content": {
-                "matched_fields": ["content.plain"],
+            "comment": {
+                "matched_fields": ["comment.plain"],
                 "type" : "fvh"
             }
         }
@@ -590,7 +590,7 @@ GET /_search
 
 The above query wouldn't highlight "run" or "scissor" but shows that
 it is just fine not to list the field to which the matches are combined
-(`content`) in the matched fields.
+(`comment`) in the matched fields.
 
 [NOTE]
 Technically it is also fine to add fields to `matched_fields` that
@@ -606,7 +606,7 @@ There is a small amount of overhead involved with setting
 --------------------------------------------------
     "highlight": {
         "fields": {
-            "content": {}
+            "comment": {}
         }
     }
 --------------------------------------------------
@@ -615,8 +615,8 @@ to
 --------------------------------------------------
     "highlight": {
         "fields": {
-            "content": {
-                "matched_fields": ["content"],
+            "comment": {
+                "matched_fields": ["comment"],
                 "type" : "fvh"
             }
         }