Small Fixes

I've been playing this version of GLAIVE with my friends for almost two months. You'd think we'd have found and fixed all the small problems by now. 

Heck no. First rule of Itch.io: find a dozen things to fix/change five minutes after you release something to the public. Argh!

-Changed the word "caster's" to "PC's" in the terminology section of pg14.

-Changed the XP required to reach a new level from "500 x [L]" to "250 x [L]". Honestly, this one is super arbitrary. Make that number whatever you want it to be to suit the pace of the game you run.