Add multiset-remove-all

[jackfirth]

Signature:

(multiset-remove-all [set multiset?] [elements (sequence/c any/c)]) -> multiset?

Examples:

> (multiset-remove-all (multiset 1 1 1 2 2 3 3 3) (list 1 2 3 2))
(multiset 1 1 3 3)

Optionally, it can include some optimizations in the case where elements is a set or multiset.