Implement `Semigroup` instances

[marcosh]

Implement several semigroup instances

• [ ] Booleans with &&
• [ ] Booleans with ||
• [x] List
• [x] string
• [ ] Semigroup A => Semigroup Maybe<A>
• [ ] Semigroup A => Semigroup IO<A>
• [ ] Int with +
• [ ] Int with *
• [ ] Float with +
• [ ] Float with *
• [ ] Last
• [ ] First
• [ ] Semigroup A => Semigroup B -> A
• [ ] Semigroup A, Semigroup B => Semigroup Pair<A, B>
• [ ] Either