chore(v3): create ffi.py

Import close to 400 functions exposed by the Rust library into the
`ffi.py` file. All of them (save `version`) solely raise a
`NotImplementedError`. The documentation of the functions has been
automatically imported from the exposed docstring by the `pact.h`
header.

Signed-off-by: JP-Ellis <[email protected]>

Author: JP-Ellis