type => $type for spec consistency
Fix featuresAt layer param
Inline render test comparisons / output generation

Instead of shelling out to a python script at the end, do the
work in JS as we go. This lets e.g. `node test/render.test.js geojson`
work as expected.
Fix geojson rendering test (fixes #891)
Merge pull request #893 from mapbox/featuresAtFixes

featuresAt fixes
Merge remote-tracking branch 'upstream/mb-pages' into mb-pages