Add new Mapbox externals with built in Leaflet
Switched out Leaflet for Mapbox
Refactored all Leaflet usage to built in mapbox.js API tools
Removed NPR utfgrid library, no longer needed
Removed all leaflet files
bump mapbox to v1.0.2
Merge branch 'v0.6.0-prep', mapbox.js 1.0 (v0.6.0)