Find intersections between routes/segments

[matt-wallis]

The is necessary in order to be able to discover how to go from A to B where A is on one segments, and B on another. i.e. it is needed for journey planning.

Implementation

Use a line-sweeping algorithm to find the intersections of all line segments. If we can't find an existing javascript implementation, then the following paper looks as if it describes a suitable algorithm:
Bartuschka, U.; Mehlhorn, K.; Näher, S. (1997), A robust and efficient implementation of a sweep line algorithm for the straight line segment intersection problem.
This may require that we also have a library for arbitrary precision arithmetic -- look at mathjs.