Endless Game. Allow user to continue the game.

- main.css isn't compiled
- a special class `.tile-gold` is added to tiles above 2048
compile main.css
Endless Game. Allow user to continue the game.

- main.css isn't compiled
- a special class `.tile-gold` is added to tiles above 2048
compile main.css
add touchend event (see PR #32)
Update refs
merge infinite game
refactor code
rename GameOver to GameTerminated to avoid ambiguity
rename tile-gold to tile-super
add styling for super tiles
rename keep playing to keep going