Added HTML5 Geolocation API example

- All demos now get Firebase from the CDN so it is easier to update in
the future
- Added link to Firebase ref for each fish example
- Added HTML5 Geolocation API example (which also demonstrates
Firebase’ onDisconnect() method)
- Updated text in example index.html and README
Merge pull request #30 from firebase/html5_geolocation

Added HTML5 Geolocation API example