Rewrote MXRequestManager for Composer integration + PSR-2 compliant

Please note that this commit is just a patch.
According to semantic version syntax, if you clone/update the repo,
nothing is backward compatible. But meh... If you're using the file
itself just like before, it's exactely the same ;)
Nasty trick to make it PSR-0 compatible AND backward compatible with "MXRequestManager" class name
Added parameter to methods to output array instead of object
Set v1 for composer. Enjoy !
Some changes on README
Merge branch 'composer'