* riece-options.el (riece-addons): Insinuate riece-mcat by default.
* riece-addon-modules.el (riece-addon-modules): Add riece-mcat.
* riece-mcat.el: Implement add-on interface.
+ (riece-mcat-alist): Removed.
(riece-mcat-description): New constant.
(riece-mcat-insinuate): New function.
(riece-mcat-uninstall): New function.