Some functions from upstream VIM were reintegrated for this:
- get_option_value_strict
- set_option_value_err
- set_option_value_for
- unset_global_local_option
The vimscript object conversion function was adapted from the version found in
'if_py_both.h' in the upstream source. It was also required to re-add the
`dict_lookup` function that was lost during the initial import.
- Split functions with multiple files in the 'api' subdirectory
- Move/Add more types in the 'api/defs.h' header
- Add more prototypes
- Refactor scripts/msgpack-gen.lua
- Move msgpack modules to 'os' subdirectory
