Stop using the protocol interpreter interface

[ejgallego]

As of now, PyCoq uses SerAPI interpreter interface; we should stop using it, and instead, generate the Coq object directly from a ML-style direct API.

The reason SerAPI used an interpreter is indeed because of the need to do RPC; however, PyCoq has no need as it has direct access the the Python runtime so going to the interpreted would be a waste.

This will require significant refactoring on the SerAPI side first; later on, we could, as discussed with @thierry-martinez , make the binding of the .mli file automatic.

[ejgallego]

Note this tool for the automatic binding from .ml https://github.com/mooreryan/ocaml_python_bindgen

cc: @thierry-martinez