- The syntax definition was confusing because it was mixing one-of options and optional arguments which are only relevant for certain options.
- Add notes about replacement capture groups. Wording could probably be improved here. Point is, capture groups are supported, using Golang's syntax (doesn't use Caddy's placeholder syntax, which can be a gotcha)
- Add similar directives section, mainly to point out that `handle_path` can be used instead in many situations to save a line. The note about `rewrite` is kinda redundant with the small paragraph at the top though. Should we move that explanation down into `Similar directives`?