Added public urlArgs method (as suggested in #66)

urlArgs makes it possible to concat a querystring to all scripts, e.g. for cache busting purposes.
Added simple test for urlArgs method (#66)
Landed a patch for the double extension issue

I noticed that the in the last unit-test (double load), the .js extension got added twice. This patches fixes it.
Merge pull request #67 from e-sites/master

Added public urlArgs method (as suggested in #66)