Implement separate set union and set intersection monoids (and semigroups)

[MarekDudek]

Currently monoid for set is union monoid, we could use both.

[jbgi]

👍 for the intersection Semigroup.

For the intersection Monoid<Set<A>>, the zero would need to be the set of all values for that type , which would requires instance of Enumerator<A> (we have) and Bounded<A> (we don't have yet).

So this can be separated into two PRs if more manageable.

[toxyduck]

Hello, I would like to contribute. Can you explain, Why do I need to use Bounded<A> for intersection monoid zero, if Enumerator<A> can provide max and min elements?

[jbgi]

max and min in Enumerator only return Option values and thus this is not very practical to instanciate the intersection Monoid. We could pass min and max explicitly though and not create Bounded for now.