Add UtfGridComposite that can composite UtfGrid tiles (MapnikGrid)
Add UtfGridComposite that can composite UtfGrid tiles (MapnikGrid)

Blechhirn/TileStache,mojodna/TileStache,mpuig/TileStache,robpvn/Vector-Tile-Research,SEL-Columbia/TileStache,MetGIS/TileStache,Blechhirn/TileStache,SEL-Columbia/TileStache,TileStache/TileStache,mpuig/TileStache,mojodna/TileStache,TileStache/TileStache,moskvax/TileStache,MetGIS/TileStache,jbants/TileStache,TileStache/TileStache,Blechhirn/TileStache,robpvn/Vector-Tile-Research,jbants/TileStache,Billups/TileStache,Kosta-Github/TileStache,mapzen/TileStache,Billups/TileStache,mapzen/TileStache,moskvax/TileStache,Billups/TileStache,robpvn/Vector-Tile-Research,Kosta-Github/TileStache,MetGIS/TileStache,Kosta-Github/TileStache,mapzen/TileStache,SEL-Columbia/TileStache,jbants/TileStache,moskvax/TileStache