Merge parallel ways

[sckilcoyne]

Streets with medians or separated bike lanes result in multiple parallel ways in OSM. This can make the map more complicated to view. Also, Mapbox has limits on the number of features displayed per tile per zoom level. To show more detail at a given zoom, merging ways would reduce the number of features plotted without reducing the number of streets being displayed.

From @bpben previous project: https://github.com/insight-lane/crash-model/blob/master/src/data/create_segments.py

How to plot lines that have multiple different ratings and clearly express what is happening will be critical.

[sckilcoyne]

I don't know if this is needed for MVP. Keeping open for now as we may want to take a look again soon.