Optional Reverse Geocoding & Parsed Geocode Result

Hi there!  Great component you've got here; it's proving quite useful to me! 

I've made a few enhancements that I thought you might find useful: 

1. Added optional reverse geocoding upon marker drag.
2. Added a new parsed geocode parameter to updateCallback.
3. Added street_number & route to returned address parts.
4. updateCallback is now also triggered upon marker drag (if one is provided and  reverse geocoding is enabled).
5. Modified demo page to demonstrate the new behaviour.  

Cheers!