Tweaks to board, enclosure, repo
- Enclosure:
 * Hole size in layer 1 is now right for threaded inserts
 * Change thickness note on layers 2 and 3 to 1/8"
 * Moved lever from center of layer 3 to ensure thickness of plastic would be the same
- Board:
 * Tweak battery holder down slightly, as it was interfering with display
 * Change to rev 15
- Repo: move enclosure file to top level, per SparkFun standards