J8 Notation

  [J8 Strings]   json-string "hi"   json-escape \" \\ \u1234
                 surrogate-pair \ud83e\udd26
                 u-prefix u'hi'   b-prefix b'hi'
                 j8-escape \u{1f926} \yff
                 no-prefix 'hi'
  [JSON8]        json8-num   json8-str
                 json8-list   json-dict
                 json8-comment
  [TSV8]         column-attrs   column-types
