Fix broken links (#2227)

A few links regressed over time and we have some redirects that can be replaced
with their canonical replacement.

The Tor-Project link was a bit of a gnarly one, as they don't accept our lychee
user agent.  They do, however, accept curl, which is why I opted to use that on
a per-host basis.  In order to do that, I've created a `lychee.toml` now, and
decided to move all other settings there as well. I think it's cleaner this way.