Simplified the preloadXML function

* remove the onload function. and directly access reponseText (see
http://www.w3schools.com/ajax/ajax_xmlhttprequest_send.asp)
* remove the IE5/IE6 backward compatiblity code
Switched to asynchronous mode

note : this fix the initial loader issue in cocoonJS (though it then
stops, because of no DOMParser implementation)
Fixed touch support detection on cocoonJS
Fixed a bug with mole default position (was strangely only visible on mobile devices)
Various small audio enhancements :

* moved audo capabilites detection into a specific function (this part
would need further improvements/rewrite)
* removed sound disabling when running on mobile devices, under CocoonJS
* added support for AAC (though barely untested)
* removed cloneNode usage, and "manually" create a new audio clip (fixes
sound in CocoonJS)
Tutorial: Fix CoinEntity.onCollision() in Part 5 -- Thanks to Soelen for spotting it!

- Also small cleanups in Parts 6 and 7.
Fixed #139
Merge branch 'master' of https://github.com/obiot/melonJS
Fixed parent container size detection (thanks tokyonono!)

@see
https://groups.google.com/forum/?fromgroups=#!topic/melonjs/ho7pVFy-bto
Fixed collision bouding boxes not being used (thanks tangenstorm!)
Ticket #140 : some internal variable/function renaming to make the code less "xml" specific

JSON file will be preloaded now if the extension is changed to 'json" in
the resource file, but won't be parsed later during level loading.

Quick Wish list  :
* make the me.TMXParser more OO and Generic
* add (fake) JSON parsing to te TMXParser
Ticket #136 : renamed video system functions
Ticket #136: fixed documentation
Added a function to enable the` context.xxxImageSmoothingProperty`  when available

Should we call this one by default when scaling and maintaining the
aspect ratio ?
first-pass update of the CHANGELOG file
Added proper documentation to the me.Vector2d class
Removed the drumbox example

way too behind in terms of API…..
ticket #136: added a corresponding getScreenContext() function
Fixed the clearTile function on non visible layers (e.g. collision map)
added changes to allow specifying a flat number of px,em, etc for font sizes. Also allows comma separated font names like in CSS