Import dice library

I've now added the dice library from here:
https://pypi.python.org/pypi/dice

It allows for easy function calls with basic dice notation, which should
make it a touch easier once I start porting stuff directly from the book
rules.

There's a note in the libtcod docs though that suggests some libtcod
functions might not be compatible with other randomizers, however, so
testing is probably required to make sure it's safe.