* Update managing-fields.asciidoc
* Remove references to Groovy
* Add information about Painless
* Link to blog for additional examples
* Update managing-fields.asciidoc
Make editorial changes per @debadair's feedback.
This overhaul of the docs structure puts Kibana's documentation more
inline with the structure that is used in Elasticsearch. This will help
us better organize the docs going forward as more docs are added.
This also includes a few necessary content changes for 5.0.
