#5 The lists are slow

[Ben Lard]

If an object gets deleted, we have to traverse the
update list and the layer list - this is slow. If we
notice speed is a problem in this area, we might have
to change the data structure or enable some quick way
to modify shit without having to do traversals (like a
member pointer to the lists an object is present in...)

However, unless speed becomes a problem, this isn't
worth screwing with.

[Ben Lard]

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This has been slightly optimized by using the list.remove
vs list.erase in a loop. However, more could be done by a
different data structure entirely.