Docs: Added deprecation notice for _timestamp and _ttl

docs/reference/docs/bulk.asciidoc

@@ -131,6 +131,8 @@ operation based on the `_parent` / `_routing` mapping.
 [[bulk-timestamp]]
 === Timestamp
 
+deprecated[2.0.0,The `_timestamp` field is deprecated.  Instead, use a normal <<date,`date`>> field and set its value explicitly]
+
 Each bulk item can include the timestamp value using the
 `_timestamp`/`timestamp` field. It automatically follows the behavior of
 the index operation based on the `_timestamp` mapping.
@@ -139,6 +141,8 @@ the index operation based on the `_timestamp` mapping.
 [[bulk-ttl]]
 === TTL
 
+deprecated[2.0.0,The current `_ttl` implementation is deprecated and will be replaced with a different implementation in a future version]
+
 Each bulk item can include the ttl value using the `_ttl`/`ttl` field.
 It automatically follows the behavior of the index operation based on
 the `_ttl` mapping.

docs/reference/docs/index_.asciidoc

@@ -257,6 +257,8 @@ specified using the `routing` parameter.
 [[index-timestamp]]
 === Timestamp
 
+deprecated[2.0.0,The `_timestamp` field is deprecated.  Instead, use a normal <<date,`date`>> field and set its value explicitly]
+
 A document can be indexed with a `timestamp` associated with it. The
 `timestamp` value of a document can be set using the `timestamp`
 parameter. For example:
@@ -279,6 +281,9 @@ page>>.
 [[index-ttl]]
 === TTL
 
+deprecated[2.0.0,The current `_ttl` implementation is deprecated and will be replaced with a different implementation in a future version]
+
+
 A document can be indexed with a `ttl` (time to live) associated with
 it. Expired documents will be expunged automatically. The expiration
 date that will be set for a document with a provided `ttl` is relative

docs/reference/mapping/fields/timestamp-field.asciidoc

@@ -1,6 +1,8 @@
 [[mapping-timestamp-field]]
 === `_timestamp` field
 
+deprecated[2.0.0,The `_timestamp` field is deprecated.  Instead, use a normal <<date,`date`>> field and set its value explicitly]
+
 The `_timestamp` field, when enabled, allows a timestamp to be indexed and
 stored with a document. The timestamp may be specified manually, generated
 automatically, or set to a default value:

docs/reference/mapping/fields/ttl-field.asciidoc

@@ -1,6 +1,8 @@
 [[mapping-ttl-field]]
 === `_ttl` field
 
+deprecated[2.0.0,The current `_ttl` implementation is deprecated and will be replaced with a different implementation in a future version]
+
 Some types of documents, such as session data or special offers, come with an
 expiration date. The `_ttl` field allows you to specify the minimum time a
 document should live, after which time the document is deleted automatically.

docs/reference/migration/migrate_2_0/mapping.asciidoc

@@ -256,6 +256,18 @@ PUT my_index/my_type/1?routing=bar <2>
 <1> Routing can be marked as required to ensure it is not forgotten during indexing.
 <2> This indexing request uses a `routing` value of `bar`.
 
+==== `_timestamp` and `_ttl` deprecated
+
+The `_timestamp` and `_ttl` fields are deprecated, but will remain functional
+for the remainder of the 2.x series.
+
+Instead of the `_timestamp` field, use a normal <<date,`date`>> field and set
+the value explicitly.
+
+The current `_ttl` functionality will be replaced in a future version with a
+new implementation of TTL, possibly with different semantics, and will not
+depend on the `_timestamp` field.
+
 ==== Analyzer mappings
 
 Previously, `index_analyzer` and `search_analyzer` could be set separately,