collection of functions to provide routing directions based on Open Street
Maps and General Transit Feed Specification data. It follows (as close
as possible) the MapBox v5 directions specification.

The algorithm provides a single route between the first and last coordinate.
It works as follows:
- create a Dijkstra collection to find the shortest path
- take the sequence and split it into 'pieces'
 - each piece is a subsection of the complete route with a common 'context'.
  The 'context' is the road name or the stop name
- loop over the pieces to create instructions based on each previous, current
  and next piece

collection of functions related to the use of GTFS feed on routing
networks.