obs-NO-WS-CTL / quoted-pair

We allow anything except the excluded characters, but if we find any
ASCII other than the RFC defined printable ASCII, a NonPrintableDefect is
added to the token's defects list.  Quoted pairs are converted to their
unquoted values, so what is returned is a ptext token, in this case a
ValueTerminal.  If there were quoted-printables, an ObsoleteHeaderDefect is
added to the returned token's defect list.

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