Link RT subject tag style ticket references, i.e. "[rt.cpan.org #NNN]" and "rt.cpan.org #NNN"
Link PR#NN, PR:NN, and PR-NN to Github in changelogs

PR is often used when denoting pull requests.  The numbers share the
same sequence as GH issues.
These aren't patterns, they're substrings.  Escape any metachars.
Test new RT and Github link formats in changelogs
Merge pull request #1044 from tsibley/link-more-bug-refs-in-changes

Link more bug refs in changes