Preliminary work for #141

Todo: show it for envs, use a different icon for each thing
Free screens in last-in-first-out order.

Fixes #144.
Merge pull request #147 from eaburns/dev/invcrash

Free screens in last-in-first-out order.
Show action icon when touching envs
That test should be in update, not handle, dummy
Merge pull request #148 from mccoyst/hints

Preliminary work for #141
Make every level a bit different
Put different swords in the stones
Don't start with the best sword
Don't start with magic; place some randomly
Merge pull request #149 from mccoyst/floors

Floor changes