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".)
The reason I'm returning `t` here is because there will be a method later on that infers the proper turn based on the lanes, so that the highlighted lane markings match what's being announced. In that method, a new object was being created, so that was being returned instead. I'll check to see if a new object _does_ need to be created.

I'll change the return type to `void` here.