Rjf/248 improve ksp

[robfitzgerald]

This PR adds some new features to search:

• Yen's k-Shortest Paths implementation
• ksp termination criteria to give finer grain control over how many iterations are run
• revised route similarity function for clearer semantics + call site
• all search algorithms can receive JSON parameters from the search query
  • k, or A Star weight_factor are the first implementations

submitting this draft for any early review but I still need to test it later this week.

[robfitzgerald]

@nreinicke this is ready for review. after running, i was able to explore k=[10,20,30,40,50] and plot which set each result comes from here, colored by it's k value, for a given OD pair. here stars are the time-optimized ksp routes, triangles are the distance-optimized ksp routes, and the circles are the pareto front generated by Compass.

i don't have any other tests, so if you feel like this could use a test, let me know.

[nreinicke]

This looks good to me, it's cool to see the k paths building out the "cloud" around the Pareto front.