Takes a list of OpenStreetMap highways returned by extract_highways()
and sequentially connects closest nodes of adjacent highways until the set of
highways connects to form a cycle.
Usage
get_highway_cycle(highways)
Arguments
highways
A list of highways as returned by extract_highways(), each
element of which is a list of distinct segments for a particular OSM highway.
Value
A modified version of highways, extended by the addition of
connecting nodes.