[doc] fix warnings/errors in doc build
- fix links to images
- fix a couple of typos
- re-add IDownloadableOneLineView doc
- rename documenting.rst back to .txt, it's intended as a doc of how to
write rst, not part of the rst doc
Related to #4832808
# -*- 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 precreate script, executed at instance creation time or when
the cube is added to an existing instance, before the schema is serialized.
This is typically to create groups referenced by the cube'schema.
"""