Merge branch 'ja/doc-commit-markup-updates'

Doc updates.

* ja/doc-commit-markup-updates:
  doc: migrate git-commit manpage secondary files to new format
  doc: convert git commit config to new format
  doc: make more direct explanations in git commit options
  doc: the mode param of -u of git commit is optional
  doc: apply new documentation guidelines to git commit

diff --cc builtin/commit.c
Simple merge