Optionally skip frame parsing with the 'skip_frames' option

[Grantismo]

This PR introduces the optional skip_frame option to the Game constructor (similar to https://github.com/hohav/peppi). This is a noop for all existing callers.

This implementation requires a seekable stream, but again this only impacts callers passing the new option.

Profiling on a sample of 187 replays:

original:
289730206 function calls (289729400 primitive calls) in 234.178 seconds
w/ skip_frames:
185392 function calls (184586 primitive calls) in 0.240 seconds

[hohav]

Closing in favor of #41.