Add tests for Carto JSON object and Mapnik XML string as sources.
Add tests for Carto JSON object and Mapnik XML string as sources.

paulovieira/tilelive,mapbox/tilelive.js,nyurik/tilelive.js,mapbox/tilelive,Norkart/tilelive.js,topwood/tilelive,gravitystorm/tilelive.js,kyroskoh/tilelive,tomhughes/tilelive.js