Add Illustrator PDFs to repository
Tweak tutorial background
Array of levels and allow restarting level

Level setup code moved into restartLevel()

Level information including board, background image and starting
positions moved into levels.js.
Add multiple levels and advance between them.

Press enter after winning to go to next level. Press R at any time to
restart level. Show messages at death or completion to prompt user.

Made two additional tiny levels. No backgrounds for them yet.