remove race condition, single url only, new events.

fix for #10 that at the moment removes the multiurl options as they were adding complexity and I wasn't convinced of the benefits.  I also changed the events as the current 3 events didn't make sense and just used the events from @leplatrem 's leaflet-spin layer as a guide, also that they could be used together in an easier way. 

I may add back the multi url after testing but am unsure as of yet.