[RichString] Add markdown support Supporting markdown requires the 'Markdown' python packages, and since it widely available on the target platforms adding it as a strong requirements will not be a big constraint. Closes #3814302

# -*- coding: utf-8 -*-
# copyright %(year)s %(author)s, all rights reserved.
# contact %(author-web-site)s -- mailto:%(author-email)s
#
%(long-license)s
"""%(distname)s repository side views, usually for notification"""