Alec Theriault authored Aug 21, 2018 and Ben Gamari committed Aug 21, 2018

This drastically cuts down on the number of Haddock warnings when making
docs for `base`.  Plus this means more actual links end up in the docs!
Also fixed other small mostly markup issues in the documentation along
the way.

This is a docs-only change.

Reviewers: hvr, bgamari, thomie

Reviewed By: thomie

Subscribers: thomie, rwbarton, carter

Differential Revision: https://phabricator.haskell.org/D5055