Merge branch 'tb/show-trailers-in-ref-filter'

"git for-each-ref --format=..." learned a new format element, %(trailers), to show only the commit log trailer part of the log message. * tb/show-trailers-in-ref-filter: ref-filter.c: parse trailers arguments with %(contents) atom ref-filter.c: use trailer_opts to format trailers t6300: refactor %(trailers) tests doc: use "`<literal>`"-style quoting for literal strings doc: 'trailers' is the preferred way to format trailers t4205: unfold across multiple lines