[SDL Utility] Add 'createSquare()' and 'createTriangle()'.
[MapView] Fix issue with clearing tiles.
[ObstructionMap] Add a bit of randomness to finding an open tile.
[SDL Entity] Shapely entities.

We now have square-shaped buildings!
We now have triangle-shaped resources!
And, best of all, we now have circle-shaped entities! er.. wait, we already had that.