Make game work on iOS and handle resize events

Apparently iOS doesn't like a 4000x3000px canvas. Changing the buffer
to 2000x2000px seems to make it work.

TODO: iOS is still having some odd caching behavior I think. Try
implementing the HTML5 cache manifest to fix it.

There was also a home screen icon added for iOS. It could use some
more work. Currently it's just one of the player graphics. It could
have the iOS shine removed possibly.

Also, code for handling window resizing was added. This also
simplifies entering fullscreen, the same code can resize the game on
entering fullscreen.

BUG: Chrome seems to not ever update window.innerHeight or
window.innerWidth after entering fullscreen until the tab is closed.
This causes the game to not be sized correcty, even after reloading.

TODO: Add a message prompting the user to enter fullscreen.
Improve motion blur

Fix horizontal motion blur by drawing in the direction the player is
moving last. Prior to this it looked like they were moving backwards.
Don't restart on enter if both won and dead
Improve camera behavior

Make camera track center of board and players.

Also add 5 as a new fake board value. Use to force centering of board
to include background.
Finish initial level backgrounds