Merge branch 'kh/branch-ref-syntax-advice'

When git refuses to create a branch because the proposed branch name is not a valid refname, an advice message is given to refer the user to exact naming rules. * kh/branch-ref-syntax-advice: branch: advise about ref syntax rules advice: use double quotes for regular quoting advice: use backticks for verbatim advice: make all entries stylistically consistent t3200: improve test style