Only count a win if both players are not currently moving
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.
Tweak level 3
Change background of levels 2 and 3 to a transparent image
Changed goal blocks to be a new sprite.

Goal blocks are a new yellow block image. Old yellow blocks removed
from standard blocks.