version bumped to 2.1.0 !

2.0.0 branch release :
https://github.com/melonjs/melonJS/tree/2.0.0
version bumped to 2.0.1
`grunt clean`: fixed the img folder not being removed
[#606] replaced the magic numbers by proper constants when updating the shape perspective to isometric (thanks ldd!)
updated CHANGELOG
merged 2.0.x into master
[#600] more accurate frame duration in the `requestAnimationFrame` polyfill
fixed audio looping (currently broken in the last howler 2.0 beta)

`me.audio.play("myTrack", true);` was not working, I realized that when
looking if ticket #473 was still applicable (and yes it is as well, as
the callback is not fired at all)
the bug is also already referenced on howler side :
https://github.com/goldfire/howler.js/issues/227
[#473] fixed callback not being repeatedly when looping a sound

not part of the ticket, but I also removed the private 4th parameter
that was allowing to define a callback to retrieve the sound id (first
this event is not supported anymore, and now it is returned by
me.audio.play)
CHANGELOG udate
[#475] cleaned the onend callback when stopping a sound
Merge remote-tracking branch 'origin/2.0.x'
removed the old comment :P
removed osbolete/dead code in me.auido
added a `me.audio.fade()` function
Merge branch '2.0.x'