Fix track limits when detecting collisions

One-off error caused and IndexError when trying to access a location out
of the the track.
Fix car location named tuple

The named tuple was not created properly, and the class with mutable
variables was sent to the drive function, instead of a imutable named
tuple.
Fix get_obstacle when x or y are negative

Accessing python list with negative values return items from the end of
the list instead of raising IndexError. This patch raise helpful error
in this case.
Merge pull request #53 from nirs/fixes

Fix various bugs