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.
This commit breaks the single ingest docs file into multiple files,
factoring out the processor docs into a documentation file per
processor. This will help make this content easier to maintain.
James Rodewig
Gordon Brown
Josh Soref
Adam Thomson
Jason Tedor