Pull Request now includes Tetris!

completed: warmups
tower of Hanoi (with saving via YAML)
Mastermind(no saving, but yes AI)

Single block Tetris, with high scores saved, plus a difficulty setting as well. (Boring under about level 8).
In general the game looks great when rendered, and the gameplay mechanics work 100% as they're supposed to.  You definitely have a ton of experience coding Ruby, so I didn't see any actual problems at all.  My comments were just various ways to maybe extract data into the right classes along with a few other very minor tweaks.  All in all though, great job!