Splitting off MIME parsing primitives

Hi,

back when slrn first gained MIME support I made a (private) fork
of mime.sl and improved and extended it over time up to a point
where it can now handle arbitraily nested multipart/* and
message/rfc822 automatic conversion of non-MIME parts to
text/plain via mailcap and much more. I've recently cleaned it up
a bit in order to publish it and now I wonder if it would be ok
to split off the MIME parsing primitives in mime.sl into a
seperate library so that it can be resused by MIME handling
macros such as mine instead of having to copy these parts?
The following patch does just this.
-- 
Guido Berhoerster

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