doc: several minor documentation improvements

This is a series of 4 loosely related documentation fixes.

1. doc: wrap links in <> — fixes links that were broken due to inclusion of the trailing dot (note how the doc has it incorrect now), simplifies a pair of occurances of []().
2. doc: fix pr-url in repl.md — Now it points to the actual pr, not to /compare/, that was invalid.
3. doc: use reserved domains for examples in url.md — changes non-reserved domains to reserved ones in url.md, per ref.
4. doc: fix url example to match behavior — fixes #22653 (closed).

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• documentation is changed or added
• commit message follows commit guidelines