Summary:
- Mention static pointers in "stolen syntax"
- Suggest importing Constraint and IsString from Data.* instead of GHC.*
- Remove obsolete SPECIALISE syntax; it was removed in or before 1999
  (d66d409b)
- Fix link in pattern signatures

Test Plan: build

Reviewers: bgamari, takenobu

Reviewed By: takenobu

Subscribers: rwbarton, carter

Differential Revision: https://phabricator.haskell.org/D5132