Implement pathfinding

[Indy2222]

After #11 is implemented adapt it to proper object movement.

There are several requirements:

• Do not go across terrain obstacles.
• Avoid all solid object, static and movable.

Research available algorithms. Plain A* won't work.

[Indy2222]

After doing a bit more research, I decided to go with a version of NavMesh in the first iteration:

1. compute rectangular bounding box around all static obstacles
2. erode map boundaries & dilate the bounding boxes
3. compute constrained Delaunay triangulation
4. create edge visibility graph from -- edges which are part of the same triangle are neighbors in the graph
5. build an R-tree for use in search for initial and target edges neighboring from/to points
   • Overlap Minimizing Top-down Bulk Loading Algorithm
6. find shortest paths with a modified A* combined with gradual funnel algorithm