Fix includes.
Add some files to "clean" make target.
README updated.
Add node.geojson() function.
Rewrote public-transport demo to use GeoJSON instead of Spatialite.

Also renames way.nodes() function to node_refs() and adds node_coordinates()
functions. Not the best interface but hopefully more efficient than having
one function that returns refs and coordinates when most of the time only
one is probably needed. But we need to evaluate this.