almost identical.
* Merge strchr(3) and strrchr(3) to strchr(3) since the two functions
are almost identical.
* Make the wording of index(3) and strchr(3) more similar.
* mdoc(7) cleanup.
Submitted by: SUZUKI Koichi <metal@gc5.so-net.ne.jp>, keramida, myself
PR: docs/32054
Reviewed by: ru
Approved by: ceri (mentor)