Added clipping flag to PostGeoJSON provider and documented everything
Added clipping flag to PostGeoJSON provider and documented everything

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