mime4cl: implement wrapping of parameters in e.g. Content-Disposition

E.g. consider the following headers for a mime part generated by mblaze:

Content-Disposition: base64;
 filename*0*=UTF-8''w8d54jn833rb8d1cbajmzkm1w1yn2f9l-all-cabal-hashes-0b0;
 filename*1*=765b.tar.gz
Content-Type: application/gzip
Content-Transfer-Encoding: base64

Currently, mime4cl will come up with the following MIME-DISPOSITION-PARAMETERS for it:

((filename*0* . UTF-8''w8d54jn833rb8d1cbajmzkm1w1yn2f9l-all-cabal-hashes-0b0)
 (filename*1* . 765b.tar.gz))