Merge branch 'la/trailer-test-and-doc-updates'

Test coverage for trailers has been improved. * la/trailer-test-and-doc-updates: trailer doc: <token> is a <key> or <keyAlias>, not both trailer doc: separator within key suppresses default separator trailer doc: emphasize the effect of configuration variables trailer --unfold help: prefer "reformat" over "join" trailer --parse docs: add explanation for its usefulness trailer --only-input: prefer "configuration variables" over "rules" trailer --parse help: expose aliased options trailer --no-divider help: describe usual "---" meaning trailer: trailer location is a place, not an action trailer doc: narrow down scope of --where and related flags trailer: add tests to check defaulting behavior with --no-* flags trailer test description: this tests --where=after, not --where=before trailer tests: make test cases self-contained