Disambiguate between URL templates and TileJSON sources

[mojodna]

node-tilejson should be used for TileJSON sources (mojodna's fork includes support for tilejson+http:, etc. protocols).

If prefixing the transport with tilejson+ isn't preferable, this module can distinguish between a URL template and a TileJSON URL by assuming that non-templatized URLs (i.e. not containing {z}, {x}, {y}) will return TileJSON.

[mojodna]

(The primary reason for this is to allow tessera and TM2 to use the same project.yml for styles using HTTP-accessible data sources.)

[elwino-cof]

I'm trying to use a Mapzen vector tiles source in my TM2 project.yml with Tessera (replacing mapbox streets vector tiles). Looks like the vector tiles are loaded properly from Mapzen server, but the raster images are empty. No error messages. Any tips or guidance would be appreciated.