Initial submit of maki icon set.

These icons are the mapbox maki icon set (https://www.mapbox.com/maki/)
released under the Creative Commons license.  The SVGs were optimized
using svgo: https://github.com/svg/svgo.  While largely for use in
implementing the GeoJSON simplestyle specification (https://github.com/mapbox/simplestyle-spec),
they provide a good base set of icons for maps in general.
First cut at Maki placemark generation code.

Still needs doc, tests, and lots of cleanup.