Add GeoJSON features with simplestyle styles in a tilelive pipeline.
npm install --save tilelive-overlay
overlaydata://GEOJSONSTRINGoverlaydata://2x:GEOJSONSTRING(retina)
Provides a overlaydata://GEOJSONSTRING scheme for tilelive,
which transforms GeoJSON into a Mapnik stylesheet
using geojson-mapnikify, and then provides
raster tiles of it.