Fix links to SPJ’s papers (fixes #12578)

This fixes #12578.
Update links to SPJ's papers in following files:

  * compiler/coreSyn/CoreSyn.hs
  * docs/users_guide/using-optimisation.rst
  * docs/users_guide/parallel.rst
  * docs/users_guide/glasgow_exts.rst

This commit is for ghc-8.2 branch.

Test Plan: build

Reviewers: austin, bgamari

Reviewed By: bgamari

Subscribers: rwbarton, thomie

GHC Trac Issues: #12578

Differential Revision: https://phabricator.haskell.org/D3745