Adds the following command:

/roll [XdY] - Roll X Y-sided dice

Note that the following standard notation dice expression are also supported:- df for fudge dice
- d% for percentile dice
- A ! to indicate that the dice "explode", rolling an additional die of the same size when the max value is rolled.
- A <5 or >5 (for any number between 2 and the die size - 1) to indicate that you want to count up how many dice rolled below or above the value.
- A k5 or k-5 (for any number between -999 and 999) to indicate that only the best K (for positive values) or worst K (for negative values) rolls should be counted in the result.