Add a parsing expression grammar for dice rolls.

Allows quickly getting the result of any dice roll in the form 'xDy[[+|-][xDy|i]]+'

Where _x_ is the number of dice, _y_ is the number of sides on those dice, and
_i_ is any integer.

The parser is (http://pegjs.majda.cz/) and you run it at the command line to
generate dice.js like so: `pegjs -e dice dice.pegjs`

Makes all the current random generation shit a lot cleaner, and I'm sure you
can find some interesting use for it later.