Allow saving custom rolls in rolls.js

[arturjzapater]

Right now, if members of a channel have a certain role, they can set a default roll so that when someone types "roll" without a valid expression, Yuki will evaluate the default expression instead. It might be useful to add a feature that allows members to set custom labels referring to custom expressions so that they needn't write the whole expression every time (e.g. they could write "roll attack" and assign it to the expression "roll 1d20+12 and 2d6+1d8+3").

[Avalander]

You may want to consider using the memory API for this.