Allow switching d% between 1-100 and 0-99

[blalasaadri]

In most RPGs, if you are asked to roll 1d10+1d00 for a d100 roll, that is interpreted as a value between 1 and 100, with the result of 0+00 being interpreted as 100; though there are people who instead interpret the d10 as 1 through 10 always, making (1) 0+90 the result that gives you 100.

There are however some games that actually want results from 0 to 99 (Mothership RPG comes to mind), so basically there is no extra case for 0+00; the values are just added up in any case.

It would be useful to be able to toggle between 1-100 and 0-99 (with the former probably being a sensible default).