Summary:
This patch adds documentation for record pattern synonyms (D1258) and
bundling pattern synonyms with type constructors in export lists (D1152).

There are also other small improvements motivated by #10900.

Reviewers: goldfire, bgamari, austin

Reviewed By: bgamari

Subscribers: goldfire, thomie

Differential Revision: https://phabricator.haskell.org/D1325

GHC Trac Issues: #10900