Bunch of fixes on the client page.

* Broke bucket type ops and bucket ops into separate sections.
* Added fetch_datatype/update_datatype to Key operations section.
* Moved fulltext_add/delete to deprecated section.
* Fixed deprecation notices on legacy search helpers on RiakBucket
* Added/fixed links to methods/classes in various docstrings.
* Added preferred method for accessing typed buckets to
  client.bucket()
* Corrected places where code text was output as italic.
* Tightened spacing in streaming examples where `close()` was called
  explicitly.
* Clarified optional arguments on create_search_index prototype.
* Added information about return values in get_search_index,
  list_search_indexes, and get_search_schema.
* Fixed capitalization typos on create_search_schema and param
  copy-pasteos.
* Added deprecation notices to fulltext_add and fulltext_delete
  docstrings.
* Removed unnecessary prototype on fetch_datatype
* Clarified purpose of update_datatype operation