Have .roll accept multiple dice rolls

[emmiegit]

So right now .roll only accepts one dice roll configuration. It should be able to support any number of configurations, such as:

.roll 2d20 d6

[emmiegit]

I'll attach it to this issue, but also add offsets to dice rolls.
So like, 3d6+2 rolls a d6, but adds 2 to the result, making it do 3 rolls in the range [2, 8].
The regex for the new dice roll should be something like:

(?:([0-9]+)?[dD])?([0-9]+)(?:([+-][0-9]+))?

[raylu-stripe]

so... https://github.com/raylu/sbot/blob/master/utils.py#L24
supports advantage, exploding dice, arithmetic, etc.