* Add enrich policy common parameter
* Add enrich APIs to REST APIs index
* Add put enrich policy API docs
* Add get enrich policy API docs
* Add delete enrich policy API docs
* Add execute enrich policy API docs
As mapping types are being removed throughout Elasticsearch, the use of
`_type` in pipeline simulation requests is deprecated. Additionally, the
default `_type` used if one is not supplied has been changed to `_doc` for
consistency with the rest of Elasticsearch.
James Rodewig
Gordon Brown
Jason Tedor