Basics of next-level functionality.

Randomly generates a new target tile, refills the player's health, and changes costs on everything.
The player gets less and less energy as they go through the levels.

Might want to tweak the values.
Fix a bug where the initial square will always be lit up.
Add in highlighting for the western motion, since you can do that.
Merge pull request #3 from blueheaven/next-level

Add in functionality for level tracking, as well as randomizing where the player's target is.