Pass `use_bin_type` as argument to `packb`

This is necessary for supporting msgpack 2.0 in Neovim, which treats all strings
as `BIN`.
Update to the new "get_api_metadata" method
Use method names instead of integer ids.

Neovim no longer supports integer method ids, now use names like a normal
msgpack-rpc client
Use 'types' instead of 'classes' when inspecting api types
Use EXT type to deserialize special API types
Fix travis build for embedded mode
Update tests to use the new api_{spawn,close} functions
Updated handle the new provider infrastructure
Update to the new method of acquiring metadata from nvim
Merge pull request #26 from tarruda/msgpack2.0

Msgpack v5 support