Vampire fixes

Fixes a span class overspilling into plaintext, cleans up a commented out pointless hackaround, 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.
No, sadly my fork got hilariously borked, I need to figure out how to unfuck it and merge Urist to my fork manually (i.e. I know how to merge manually, but my code is too messed up at this point) before I can do more than single-file edits.

And anyway, I think that Calamity uses its own method of spawning antags, but I'll look into that.