/* -- RFC 2045, 6.7 --
(1) (General 8bit representation) Any octet, except a CR or
LF that is part of a CRLF line break of the canonical
(standard) form of the data being encoded, may be
represented by an "=" followed by a two digit
hexadecimal representation of the octet's value. The
digits of the hexadecimal alphabet, for this purpose,
are "0123456789ABCDEF". Uppercase letters must be
used; lowercase letters are not allowed. Thus, for
example, the decimal value 12 (US-ASCII form feed) can
be represented by "=0C", and the decimal value 61 (US-
ASCII EQUAL SIGN) can be represented by "=3D". This
rule must be followed except when the following rules
allow an alternative encoding.
*/