Even more fixes!

Thanks for those who have braved the Amulet and left comments!

I've made some fixes based on those and on my own observations.

1. Caching. I have added dictionary-based caching for sprite sheets, and an @lru_cache for the individual sprites. Based on the stats, this significantly slims the memory profile.
2. Music. @MilkExpanse was kind enough to track down an issue with the music player. I have wrapped that in an exception handler so that those without the MP3 DLL can get through that call.
3. The Second Tutorial. A few things here.
   1. Added a "sacred" item attribute. Starting character Ritz, and the archer in the second tutorial, both have this on their equipped weapons. This attribute means the item does not wear out uses when used. This means the archer, when possessed by the Amulet, will definitely have arrows with which to finish off the sprite.
   2. The "K" command will just kill everything -- I have pointed this out in a message in the tutorial. In fact, the "K" command will kill everything in every level, if that's important.

I've learned so much from this experience -- already thinking of what I can do for next year.

Thanks to all who have played!