double the icon css for Firefox
Merge pull request #74 from mapbox/firefox-icons

double the icon css for Firefox
some basic usage documentation
Update to tilelive-bridge 0.0.5 to fix handling of solid tiles on export.
Set default source to mapbox-streets-v4
Merge pull request #77 from mojodna/mapbox-streets-v4

Set default source to mapbox-streets-v4