[Cs3] erase(key) in multimaps and multisets

[Mikhail Nesterenko]

CS3 students,

It turns out erase(key) eliminates all elements with this key in the
multimap and all elements from the multisets. Hence,

	 myMset.erase('b');

Removes all 'b's from the multiset.

Thanks,
-- 
Mikhail