Added support for pyboy event conversion.

Already working for a simple example.

Added interface to custom boot ROM loading in Python.

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.

Makes use of temporary directory.

Allowing frame by frame "navigation".

Allow simple screenshot saving.