(mime-decode-parameter-value): Removed comments.

(mime-decode-parameter-value): Removed comments.
(mime-decode-parameter-encode-segment): New function.
(mime-decode-parameter-plist): New implementation.
Switched from decode-then-concat to concat-then-decode model.
(mime-parse-parameters): Strip quoted-pair in quoted-string.
(mime-parse-Content-Type): Use `make-mime-content-type'.
(mime-parse-Content-Disposition): Use `make-mime-content-disposition'.