Merge branch 'ab/trailers-extra-format'

The "--format=%(trailers)" mechanism gets enhanced to make it easier to design output for machine consumption. * ab/trailers-extra-format: pretty format %(trailers): add a "key_value_separator" pretty format %(trailers): add a "keyonly" pretty-format %(trailers): fix broken standalone "valueonly" pretty format %(trailers) doc: avoid repetition pretty format %(trailers) test: split a long line