Undocument internal legacy structures from headers

- make some older definitions fit in a single line, because
  they are no longer used internally and are intended for back compat with
  older code.
- Undocument older `lcb_create_st` member structures
- Mode `lcb_configuration_callback` stuff to the `deprecated.h` file and
  deprecate the callback accessors. These functions should not be used
  in newer code - rather the alternative `lcb_set_bootstrap_callback`
  should be used.
- Undocument internal `IOCREATEOPTS` members. Code should either
  explicitly create one from external code, or use the builtin struct
  variant.

We should really move a lot of these definitions outside of the header
files, but we need to be compatible with code as early as 2.0.0 (two
years ago).

Change-Id: I75619795e7d4a16248465dd580c3d43d6228f8e6
Reviewed-on: http://review.couchbase.org/43025
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>