Gym-super-mario-bros

Update with new `RandomStages` environment that samples stages at random.

Fix links in README for PyPi

the older iterative implementation outperforms the current vectorized numpy implementation. Reverting for the better performance (and more understandable code).

update the version of nes-py

Implement the `get_action_meanings` method in the `SuperMarioBrosRandomStagesEnv` environment.

fix the RNG name to work with gym wrappers.