Vampire fixes

Fixes a span class overspilling into plaintext, lowers the Secret reqs a bit to factor in our pop and the apparent interest in playing it, fixes the one-vamp-at-20 issue by making the game scale it upwards from 1, not zero - so that there will be two vampires for the 10-19 player range, instead of 1.
Merge pull request #121 from scrdest/patch-1

Vampire fixes