Add a loadFunction for loadurl.

The signature of submitFunction is changed so that the options are first.
This makes the two functions have compatible signatures and the same
function can potentially be used with having to type test arguments.

Update doc for the change to the submit arguments.
Use submit/loadFunction for the demo.

Replace the code that overrides the $.ajax() function with the loadFunction/submitFunction
configuration options.
The two clean tasks were conflicting.

Now there is tidy and clobber as the subtasks.