don't display entities that are not on the screen
ajout de chrono pas interactif (position du div)
chrono for the game
better chrono (start when everything is loaded and game started
README and remove assets for sound
some debug test (ghost)
debug ghost
Rider rendering : base on anchors, not positions

in replays, we save anchors which is more helpful for external reads.
key 'u' to change rendering mode
between ugly mode uglyOver mode and normal mode
changing biker rendering based on anchors

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:
	bin/xmoto.js
	index.html
	src/level.coffee
	src/level_elements/entities.coffee