[pathfinding] Document navmesh better.

[donmccurdy]

Currently docs are spread out and not interlinked. Make this coherent:

• pathfinding module
• controls docs
• misc/ folder
• navmesh blog post

^Maybe should just put all docs into README, moving forward?

[dirkk0]

That would be cool! Did you find a solution for the Navmesh creation support getting ripped out of Blender?

[donmccurdy]

Working on it. 😉

[dirkk0]

Great, thanks!