Added throttling of Overpass API requests (partially implements #39)
Disabled debug in example
Merge pull request #53 from mkeblx/url-hash

URL coords
Updated readme with coordinates in URL
Limit to 1 XHR request for now
Set location to Heathrow Airport
- Turned City.init into a promise
- Added camera pan and orbit caps
- Moved gridUpdated listener into DataOverpass so it's not inherited by all children of Data
- Added aerodrome tag from OSM
- Refined OSM heights
- Expanded the floor
- Added ability to remove objects from the scene
Removed Heathrow coords from example