Added soothsayer

I'm not entirely sure whether you want a pull request for gh-pages as well, or if you just want to re-deploy that yourself, but it should be the same either way, right?

Anyway, I just wanted to test a strategy involving Soothsayer, and since it wasn't implemented I added it. Works fine at http://amalloy.github.io/dominiate/play, including the "don't draw if you didn't gain a curse". It should work with Trader also (ie, if you gain a Silver instead, you don't draw)..