Add TMX map support (barely.)

Yep.  This is messy as hell but it works with my test map and right now,
that's enough to make me smile.

Signed-off-by: suicidepills <atom.mac@gmail.com>
tmx-map.js code clean-up, docs/comments.

Signed-off-by: suicidepills <atom.mac@gmail.com>