[doc] Move mapper attachment plugin to mapper page

docs/plugins/api.asciidoc

@@ -15,12 +15,6 @@ The delete by query plugin adds support for deleting all of the documents
 replacement for the problematic _delete-by-query_ functionality which has been
 removed from Elasticsearch core.
 
-https://github.com/elasticsearch/elasticsearch-mapper-attachments[Mapper Attachments Type plugin]::
-
-Integrates http://lucene.apache.org/tika/[Apache Tika] to provide a new field
-type `attachment` to allow indexing of documents such as PDFs and Microsoft
-Word.
-
 [float]
 === Community contributed API extension plugins
 

docs/plugins/mapper.asciidoc

@@ -8,6 +8,12 @@ Mapper plugins allow new field datatypes to be added to Elasticsearch.
 
 The core mapper plugins are:
 
+https://github.com/elasticsearch/elasticsearch-mapper-attachments[Mapper Attachments Type plugin]::
+
+Integrates http://lucene.apache.org/tika/[Apache Tika] to provide a new field
+type `attachment` to allow indexing of documents such as PDFs and Microsoft
+Word.
+
 <<mapper-size>>::
 
 The mapper-size plugin provides the `_size` meta field which, when enabled,