DOC: Improve documentation of http-re(quest|sponse) replace-(header|value|uri)

- Clarify that everything and not only the matched part is replaced (GitHub #328)
- Reduce duplication and inconsistencies by referring to a single canonical directive
  that includes everything one needs to know about.
- Fix indentation

(cherry picked from commit 2252beb8557d73407b8f96eef91d6927fb855685)
Signed-off-by: Willy Tarreau <w@1wt.eu>
1 file changed