Fix broken links

[petdance]

Running broken-link-checker on beyondgrep.com gives us these errors:

$ blc -r https://beyondgrep.com/ | ack 'Getting|BROKEN'
Getting links from: https://beyondgrep.com/
Getting links from: https://beyondgrep.com/why-ack/
├─BROKEN─ http://www.unixlore.net/use-ack-as-better-grep.html (HTTP_403)
├─BROKEN─ http://www.just-another.net/ (HTTP_404)
├─BROKEN─ http://www.prescod.net/ (HTTP_404)
Getting links from: https://beyondgrep.com/install/
├─BROKEN─ https://beyondgrep.com/documentation/ack-2.28-man.html (HTTP_404)
├─BROKEN─ https://chocolatey.org/packages/ack (HTTP_404)
Getting links from: https://beyondgrep.com/documentation/
Getting links from: https://beyondgrep.com/community/
Getting links from: https://beyondgrep.com/more-tools/
Getting links from: https://beyondgrep.com/changes.txt
Getting links from: https://beyondgrep.com/ack-v3.1.0
Getting links from: https://beyondgrep.com/documentation/ack-1.96-man.html
├─BROKEN─ https://beyondgrep.com/Win32/Console/ANSI.html (HTTP_404)
├─BROKEN─ http://annocpan.org/dist/ack (HTTP_403)
├─BROKEN─ http://www.shellarchive.co.uk/content/emacs.html (HTTP_404)
Getting links from: https://beyondgrep.com/documentation/ack-v3.1.0-man.html
├─BROKEN─ https://perldoc.perl.org/perlreref.html%7Cperlreref (HTTP_404)
├─BROKEN─ https://perldoc.perl.org/perlretut.html%7Cperlretut (HTTP_404)
Getting links from: https://beyondgrep.com/why-ack/index.html
├─BROKEN─ http://www.unixlore.net/use-ack-as-better-grep.html (HTTP_403)
├─BROKEN─ http://www.prescod.net/ (HTTP_404)
├─BROKEN─ http://www.just-another.net/ (HTTP_404)
Getting links from: https://beyondgrep.com/install/index.html
├─BROKEN─ https://chocolatey.org/packages/ack (HTTP_404)
├─BROKEN─ https://beyondgrep.com/documentation/ack-2.28-man.html (HTTP_404)
Getting links from: https://beyondgrep.com/documentation/index.html
Getting links from: https://beyondgrep.com/community/index.html
Getting links from: https://beyondgrep.com/more-tools/index.html

[n1vux]

good chance most of those (aside from our own obsolete pages) can be patched with archive.org WaybackMachine links.

[petdance]

For some that might be a good option. For others, the links are just bad anyway.