Support for PyPi

Closes #43

See merge request !44

Without flush we would might be loosing some bytes in writing.
This is explicitly stated in https://doc.rust-lang.org/std/fs/struct.File.html.

Also adds more explicit error handling in state related code.

Also adds flush operation after writing to file.

Allows speedup and FPS measuring.

Uses a different file for the C structs of Libretro.
Makes it easier to manage the structure these structures.

Fix Libbretro issue in loading of base emulator info

See merge request !43

Was creating major memory issues, including in the save of state files.

Adds warning on failing to set callbacks.

Should allow simple testing of the core.

There's a new rust stable version.

Allows better understanding of the message.

More standard support for the `BusComponent` interface.

Allows blargg's test ROM to pass.

This reverts commit 193f61a2.

This should fix a cargo network issue.