Overhaul import logic and stop using projected coordinates

[dabreegster]

This PR is a breaking change to the binary graph file format:

• Instead of storing Mercator coordinates and doing transformations everywhere, just store raw WGS84 coordinates. This gets rid of dependencies on old A/B Street libraries, and solves bugs where the computed route length is wrong for large areas. Closes Remove geom dependency #5.
• Removes the dependency on osm2streets, instead importing from OSM XML or PBF using a much lighter-weight library. Closes Build from something closer to raw OSM #21.

Note this takes a dependency on georust's current boolean ops, which're known to have panics. I haven't hit any in my few simple tests so far, but if I do when updating a large user of this tool, I'll probably cut over to georust/geo#1089 and take any performance hit.