Rename AStarWithCallback to AStarPathWithCallback

It's good to have Path in the object's name, though it starts to look a bit
convoluted now.

Names are hard.
Implement AStarPathWithMap

A complement to the callback variant, this uses tcod::Map as the source of
truth.
Fix out of bounds safety issues with path.get

Calling TCOD_path_get when the index is out of bounds causes invalid memory
access.
Implement Dijkstra path finding
Merge AStarWithCallback and AStarFromMap
Merge Dijkstra path structs

Just like we did for A*.
Merge pull request #10 from tomassedovic/safe-path

More path finding