* Map is unnecessary and inefficient in almost every case.
* Replaced by the new HashMap.
* Renamed Map to RBMap and Set to RBSet for cases that still make sense
(order matters) but use is discouraged.
There were very few cases where replacing by HashMap was undesired because
keeping the key order was intended.
I tried to keep those (as RBMap) as much as possible, but might have missed
some. Review appreciated!
* Renames for 2D and 3D
* Class name was confusing, given both 2D and 3D have a "visible" property that is unrelated to actual on-screen visibility.
* New name makes it clear that this is about visibility on screen.
