[maintenance] self-linkcheck the Sphinx documentation.

[jayaddison]

Feature or Bugfix

• Bugfix

Purpose

• Fixups for a few broken links in the Sphinx documentation, as found using the linkcheck builder.

Detail

• Generic Mapping Tools: moved from being hosted on a subdomain of .edu to its own dedicated domain.
• Leo Editor: domain appears to have expired; GitHub pages is available alongside source repository.
• Ring Programming Language: Sphinx docs are hosted on GitHub; no 'latest' link available as far as I could tell, so this link is to v1.20 (current at time-of-writing).
• simuPOP: Static hosting on SourceForge evidently no longer working; checked the mailing list and found a GitHub repo with documentation available on GitHub pages.
• SqlKit: could not find any remaining hosting for this project -- there is an unrelated Swift project with the same name,
• DJ-Stripe: HTTP redirect is currently broken; link to source project repository's GitHub pages, which host the project's homepage.
• QuTiP: page not found; use RTD link instead.
• Transiflex CLI: fixup for rST hyperlink target.

Relates

• N/A

[chrisjsewell]

Great cheers!

[jayaddison]

Thanks!