- code cleanup
- Coordinate.zoomTo method moved to geotiler.geo module as `zoom_to`
  function
- removed unused Coordinate.zoomBy method
- s/IProjection.locationCoordinate/IProjection.geocode/
- s/IProjection.coordinateLocation/IProjection.rev_geocode/
- changed _find_top_left_tile function to not use Coordinate class
- removed tile downloader dependency on Coordinate class
- removed providers dependency on Coordinate class