Errata for Poisoner & Potion Master

After some more playtesting, I decided to gimp the Poisoner and Potion Master a little, giving them 1standard poison roll and two initial random potions.

Clarified a bit how Potion Master distillation and mixing work, and also cleared up how the Potion Master would use the Sling. Basically, the idea is that they would Mix potions with curses, enhance them to work on skin contact, and sling them at enemies using special Sling Flasks.