Cleanup C++ BackEnd

fully reviewed code and resolved most of the bad smells

Make _skip public (i.e., skip) in FrameSkipEnv

make _skip property public (i.e., skip) so it's more intuitive that this value may be mutated by end-users.

Remove Unnecessary Featrues

Move frame skip to a separate env wrapper and remove the frame limiting mechanism

Fix Restore Feature

Set a flag when a backup is created so that reset can know to use _backup instead of _LIB.reset(self._env)

Backup & Restore Feature

Implement a state backup and restore solution for SimpleNES

Fix Dependencies for Python2

fix matplotlib dependency (>=2.0.2 instead of >=2.3.2)

Better RAM Acessor

Use a direct buffer to create a NumPy vector wrapping around the RAM for the emulator instead of issuing reads and writes through the ctypes API.

Resolve issue in setup.py for Windows

Resolve an issue in the setup file that cause windows installs to fail

Resolve Compiler Warning

Comment out an unused variable to resolve a compiler warning from clang++

Code Optimization

Optimize and refactor code for a 20% speed up.