Define the track

[rbwhitaker]

The track is 24x40 in the original game. That's a reasonable default, but we want to allow for boards of other sizes too.

• Grid-based thing to represent the squares on the board.
• The ability to represent different types of terrain (asphalt, dirt, ice, etc.)
• Each terrain type needs metadata about things like drag and/or top speed, whether crossing into it brings you to a standstill, and possibly more (color?).
• Some way to define the start/finish line, but perhaps other lines as well. For example, it might end up making sense to have each track have several lines that cross the track (only one of which is visible) and we track crossing each of several lines around the loop to ensure the player is actually going around the loop. These lines might also serve as a way to help the AI know how to make its way around the track, because it can navigate these instead of having to do freespace planning.