Items are placed and ready to pick up!

This is an alpha implementation of item pickups, but they are efficiently generated which is great for the Game Boy. They don't disappear forever, though, so I might use Pearson's Hash for a history of 256 items.

Insertion needs to be very fast. Even though picking up an item can have a little sound effect or animation, each item that can generate can't have a value in the hash table. I think simply adding x and y to form the key will work well enough, but I'll verify that 😄

Anyways, I'm happy with the progress of this game and am really enjoying working around the limitations of the Z80.