Maintain and serve a PGXN web site

Changes for 0.23.4 - 2024-02-06T23:47:18Z

• Fixed the dependency configuration in `Build.PL` so it actually knows to install modules required for testing. Thanks to Slaven Rezic for the report!
• Added a link to the GitHub repo and issues to the docs and README.
• Updated some wayward http URLs to https.