(coding-system-type): Doc-string modified.

(coding-system-type): Doc-string modified.
(coding-system-category): New function.
(make-subsidiary-coding-system): Argument BASE deleted.
(make-coding-system): Put properties no-initial-designation and
coding-category to a newly created coding system.
(define-coding-system-alias): Put property parent-coding-system
to a new alias, property alias-coding-systems to a parent.