[Email-SIG] fixing the current email module

[Stephen J. Turnbull]

Barry Warsaw writes:

 > So the basic model is: accept strings or bytes at the edges,
 > process everything internally as bytes, output strings and bytes at
 > the edges.

In a certain pedantic sense, that can't be right, because bytes alone
can't represent strings.

Practically, you are going need to say how a bytes or bytearray is to
be interpreted as a string, and that is going to be one big mess.
(MIME?)

Going the other way around you have no such problem, or rather the
trivial embedding works fine, except that you have to do a range check
at some point before you convert to bytes.