Add package for Typespeed game

I packaged the classic Typespeed typing game for Nix. By default, typespeed stores high score files and such in /var and /etc, which is problematic in Nix. I wrote a rather lengthy patch that creates a ~/.typespeed directory with ~/.typespeed/score and ~/.typespeed/config when typespeed is started.

I wasn't sure how I should add myself as a package maintainer, so I left that out for now.