docReady : var already initialized in the immediate function

And it seems to me that's the good way of doing things...
docReady : made things working when $ is called multiple times

* instead of overwriting DOMReadyCallback, we manage a queue
* the array is emptied (ie no references are kept to callbacks,
  because that would be a potential memory leak)
docReady : jsfiddle
docReady : js file documentation "ready" for pull request
Merge pull request #13 from daviddallet/docReady-multiple_calls

jquery.documentReady.js : fix when $ is used multiple times