This updates the RMTileStreamSource to be more in line with MapBox's current offerings. We're finding that most users are simply wanting to use the MapBox Streets layer, as Foursquare now is, but we want to still retain configurability for other tilesets and custom, local TileStream servers.
MapBox source revamp (class rename, TileJSON support, iOS 5+)
fix filename in comment header
fix tile cache key
Closing this for now. Needs some more work.
fixes #172: add background fetch tile count API