[Cs3] set update operations

[Mikhail Nesterenko]

CS3 students,

This is regarding the question on set update operations. They are
indeed similar to map update.

For set insert, there is an insert with element (shown during class),
there is alos inset with an interator hint and insert with iterator
range.

Insert with element returns the pair containing an iterator and
success or failure of insertion.

For erase, there is an erase with element, erase with iterator, erase
with iterator range.

I updated the slides to make it more detailed.
-- 
Mikhail