Add support for reading in lanes that have multiple turns

At this point, there may be cases where all the displayed lanes are green. For example, if you're taking a left turn at a standard (90-degree) intersection, and there's a right-turn island, then for the segment leading up to the island, all displayed lanes will be green.

This will be fixed later when support is added for having 90-degree turns with `turn:lanes` info displayed and when the turn lane information is copied to nearby intersections before the main turning intersection.