Pycept cleanup

@subutai - please review

This does the following:

1. Uses API key from environment if you don't pass one to the constructor.
2. Updates the README to reflect change to new API. (fixes #16)
3. Does some style cleanup to match Numenta style guide - Subutai please let me know if we decided to use a more canonical Python format instead of the Numenta style guide (I saw a lot of snake_case variables).