* Reorganize MapEngine
This is already turning into a mess...
* Map engine selects tile index to use
Still very ugly
* Fix subtile flag combination
* Prepare randomly generated base tiles
* Restore collision viewer
* Movement works again, searches for straight paths
Paths are now d2vector slices
* Fix LOS calculation
* Fix test (I think)
* Comments and newlines in engine.go
* Comments and newlines in object.go
* Comments and newlines in animated_entity.go
* Comments and newlines in missile.go
* Comments and newlines in npc.go
* Comments and newlines in player.go
* Removed object.go (incorrectly merged it in during rebase).
* Comments and newlines in renderer.go.
* Comments and newlines in map_entity.go.
* Comments and newlines in walk_mesh.go.
* Comments and newlines in viewport.go and tile_cache.go.
* Comments and newlines in stamp.go and wilderness_tile_types.go.
* Comments and newlines in everything else.
* moved filter constants back to d2enum
* moving key and mouse button enums into d2enum
* moving render type enum into d2enum
* moving input even priority enums into d2enum
* moving terminal enums into d2enum
