debug assertions for copy_fast

Support for SIMD operations for RGG1555

Closes #45

See merge request !45

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.