Test formatting (added newlines)
Test formatting (remove Coffeescript added returns)
Added onNodeInitialize event (closes #21)
Do not check if callback is a function, but just if it is not 'null'.

Rationale: the jQuery.isFunction function is nice but not really
necessary in this case. A simple !== null check will do fine and is
better for performance. I leave the responsibility of not passing a
non-function to one of the event settings to the developer using this plugin.