Rust Pathfinding

We're messing around with pathfinding implementations (which will eventually be put into a 3D environment)

We're rather dumb right now, however, so don't expect anything working for the next few days.

Checklist:

• Generic PathSolver layout (generic to the max!)
• AStar implementation (untested, but we don't make mistakes)
• Proper implementation (world environment and what-not) [not done]