Merge branch 'rr/shortlog-doc'
Update documentation for "log" and "shortlog".
* rr/shortlog-doc:
builtin/shortlog.c: make usage string consistent with log
builtin/log.c: make usage string consistent with doc
git-shortlog.txt: make SYNOPSIS match log, update OPTIONS
git-log.txt: rewrite note on why "--" may be required
git-log.txt: generalize <since>..<until>
git-log.txt: order OPTIONS properly; move <since>..<until>
revisions.txt: clarify the .. and ... syntax
git-shortlog.txt: remove (-h|--help) from OPTIONS