Added /roll command to chat

I added a /roll command that lets you roll 2,4,6,8,10,12,20, or 100 sided dice. You can roll multiple dice by doing /roll 2d4, and it will show each roll separately and the total together. I also made it work with either /roll (1d20|d20|20|), each of these options would roll d20. Anything that doesn't match falls back to d20.