Update to MTOM specification

Dear all,

Here is a revised draft of the MTOM specification.

This draft is a first try at removing from the MTOM specification the 
description of the MIME packaging and referring to the MIFFY 
specification [1]. This draft is still in a rought state and will need 
to be improved as the MIFFY specification evolves.

The draft uses colored diffs for better showing the modifications, 
however in some places large amount of texts were removed and only the 
section title remains.

Best regards,

Hervé.

[1]