Add basic support for reading turn:lanes and drawing the turns as lanes

The announced turn being made is still the same. (For example, if, as per the lane marking, the indicated turn is a U-turn, then the announced turn is still "keep left".)
Primary and secondary are just meant to contain the first and second turns as read in. Yes, swapping them now would make it easier down the line.

Also, should it be renamed to "first" and "second"?