control index recursion; support new- and old-style ES doc formats

- Adds recursion flag to index().
- Fixed settings() URL.
- Made create_index() and delete_index() into hidden functions.
- Removed all the *_exists() functions.
- Renamed get/post/delete functions to more closely match HTTP
  request types.
- post() now supports both old-style list-of-dicts metadata format
  (ddr-local) in addition to new normal-dict format (ddr-public).
- Force explicit passing of index arg.
- ddrindex command