Support for 8BITMIME

[srittau]

See RFC 6152.

Enabled with -8 or --8-bit-mime

[slavkoja]

Yes, please add it, for now message with text:

Subject: Testovacia správa

Text tela správy ľščťž ýáíé...

becomes:

...
Subject: Testovacia =?utf-8?Q?spr=C3=A1va?=
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 8bit

E%E> C=C!C-C)...y D>E!D

AFAIK, Python (3.9 in my case) is able to deal with UTF-8 messages without problems...