Adds new fixture and trace for testing
Adds special handling for destination
Renames route engine callbacks for clarity
Converts RouteEngine to state machine.

* Adds special handling for route start and destination.
* Temporarily removes distance calculations.
Restores and improves distance calculations.
Removes unused route and trace file.
Merge pull request #281 from mapzen/chuck/fix-route-auto-advance

Improve auto-advance and distance calculations