Added layer preview configuration to API.html
Added layer preview configuration to API.html

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