Move neighbors into PathFinderConfig

By allowing this we gain the ability to switch between 2d/3d quite
flexibly. Additionally we are open for fancy things, e.g. teleporters:

-- teleport if on 42,42,42
teleport :: Coord -> [Coord]
teleport c = neighbors2d ++ if c == (Coord 42 42 42)
               then [Coord 1337 1337 1337]
               else []

Or dead ends:

isDeadEnd :: Coord -> Bool
isDeadEnd = undefined

deadEnd :: Coord -> [Coord]
deadEnd c = if isDeadEnd c
               then []
               else neighbors2d c
Add simple A* benchmarks via criterion
Extract Coords module from Types module

I think Coord has enough functionality to get an own module, somehow it
does not fit into Types anymore.

I am leaving the Types module with only Identifier though, as I did not
found another good place for it.