Simplifications, refinements and new features

These commits are mainly simplifications, refinements or new features.

WHAT I'VE DONE:
* Made Hey installable (not tested yet, however). You can run the setup script (`sudo python setup.py install`) and you should then be able to run `hey` from your command line like any other CLI apps.
* The `update` command now detects the Linux distribution, so there's no need for a user to explicitly state it.
* Made a few minor simplifications in `what.py`. For example, instead of creating a lookup dictionary to translate what's returned from `datetime.datetime.now().month` to the English month, just use `datetime.datetime.now().strftime("%B")`.
* Added dice.py. E.g., `hey roll a dice for me` can now be used.
* Added coin.py. E.g., `hey toss a coin for me` can now be used.
* Alphabetically sorted all imports. This was a very simple refinement.