Merge branch 'hm/paint-hits-in-log-grep'

Merge branch 'hm/paint-hits-in-log-grep'

"git log --grep=string --author=name" learns to highlight hits just
like "git grep string" does.

* hm/paint-hits-in-log-grep:
  grep/pcre2: fix an edge case concerning ascii patterns and UTF-8 data
  pretty: colorize pattern matches in commit messages
  grep: refactor next_match() and match_one_pattern() for external use