better game loop : physics and moto position are refreshed 60 times per second whatever the framerate of the game. So the moto behaviour is the same on any computer (or almost)
Sky is made of parallax scrolling
better numbers for sky
forgot to uncomment something
Level: object_to_follow and ugly mode

Instead of refer to the moto everywhere, the level object
now includes an object_to_follow function which will point
later on a ghost, a replay, a player.
Add the ugly mode. For the moment, only for the entities in the
master branch. The 'u' key switch from ugly, to uglyOver and normal
mode.

Signed-off-by: Nicolas Adenis-Lamarre <nicolas.adenis.lamarre@gmail.com>
Level: object_to_follow, fix sky

Signed-off-by: Nicolas Adenis-Lamarre <nicolas.adenis.lamarre@gmail.com>
merge

Signed-off-by: Nicolas Adenis-Lamarre <nicolas.adenis.lamarre@gmail.com>
Merge branch 'master' into replays

Signed-off-by: Nicolas Adenis-Lamarre <nicolas.adenis.lamarre@gmail.com>

Conflicts:
	.gitignore
	bin/xmoto.js
	src/input.coffee
	src/level.coffee