Get a directed edge given its index within the tile (do not need
entire graphid.
Outline of the A* algorithm. Still some missing pieces and cleanup
needed.
Add tests and get adjecency list working.
Merge remote-tracking branch 'origin/master' into dwn
Merge pull request #42 from mapzen/dwn

Adjacency List Updates
Merge branch 'master' of https://github.com/mapzen/valhalla into gdg