This directory will contain the built sources (iD.js, iD.css)
and images. On a release branch, we will check in the generated
files. For the osm.us/master deploy, it should run make and use
dist/ as the root.
Paths in css are relative, e.g. url(img/foo.png).
At z16 and below, tagged points are rendered with a small
dot in the center. At z17 and above, they are rendered with
a maki icon.
See the test rendering page for examples.
Fixes#381.