Omit trailing slash from URLs

[spawnia]

If the GitHub link could be updated as well we would be consistent throughout:

[benjie]

Just a note that https://example.com/foo and https://example.com/foo/ are concretely different URLs. Many servers will auto-forward from one to the other, but you cannot assume that this is the case for all URLs. One notable exception to this is the root path https://example.com and https://example.com/ which are equivalent for all websites.

I tested a few of these links and didn't find any that break, but it was not exhaustive.

[ghmcadams]

Thanks for that, @benjie.

@spawnia could you verify that all URLs changed in this PR are still accurate and working? If any are not, we can revert.

[spawnia]

All URLs are fine, except melody.sh which is entirely offline - see #217