Write some JavaScript to handle redirects on the 404 page about gpodder.github.io

[thp]

Yeah, the server isn't going away quickly, but we eventually need to handle those (I'd also be okay with dropping those redirects or replacing them with something else [some JavaScript in the 404 page that handles the redirect by parsing and matching the URL?], not sure how dynamic this can be).

[adamvoss]

HTTP redirects are not available with GitHub Pages, as you are familiar with from the podcastparser and mygpoclient pages.
HTML redirects (meta refresh) can be done (ref podcastparser/mygpoclient) as can JavaScript.

With Jekyll, (and the current state of things) to use meta refresh we would need a file for every target making it rather impractical for some of the redirects (such as commit/$sha1). Thus we will need to go with the 404 and JavaScript route. We should be able to access the full requested URL from the JavaScript so will be able to be dynamic as we need to be. The down-side is that it won't be as friendly to search engines, but I don't see that as much of an issue for the links that are affected.