WIP
Add some debugging comments
Finishes working version of lane changes

(issue #2)

Known issues:
* If the player is too far off-centre from a lane, attempting to move across that lane will cause the player to "snap" back into the same lane, causing a move that's not very large. Should this be the behaviour?
* Some bounding issues with turning and big lanes.. since we're testing for an intersection tile then checking the bounds, a situation can arise where the player is in the middle of a multi-lane T-intersection tile and tries to turn in the one direction where there *isn't* a road. The bounds checking will pass because there's still road there, but of course it shouldn't be possible!