Maybe: rewrite Libraries to be Traversals on Maps?

[issa-tseng]

in a sense, a Library#get operation is a reduction operation on a stored data structure that highly resembles a Map. but maybe this is contrived, or maybe this is a great simplification. i don't know yet.

[issa-tseng]

the more i think about this the more unlikely it is.

but also, if we drop IE support we could use WeakMaps to simplify the class registration quite a bit.