Added support for pyboy event conversion.

PyBoy interface was also updated with a mapping table.

Makes it easier to interact with the base py.rs file

Already working for a simple example.

Added interface to custom boot ROM loading in Python.

Support for Python

See merge request !36

Using pySDL2 and sending them as part of the next frame process.
There's still many TODOs pending for performance improvements.

Also changed `save_image()` method to removed auto format append in file name.

New options that allow fine grain control of how to capture a video.

Also made extension (container) and video encoder separate concepts.
More modularity to the way encoding is performed.

Also made Union more explicit, raises Python3 compatibility.