[#507] Remove Object.prototype.mixin, as it creates a compatibility issue with other libraries (notably socket.io)

- This method is not used anywhere in melonJS core.
- keep melonJS lightweight! [#212]
[#507] Update CHANGELOG
CHANGELOG: fix some old typos.

Conflicts:
	CHANGELOG
Normalized the CHANGELOG
Fixed a space
Merge pull request #511 from aaschmitz/1.0.x

Normalized the CHANGELOG
Sync'ed with the last 1.0.1 branch