[book] remove dbapi documentation Move some still-relevant doc related to the RQL connection API to the 'sessions' section. It might make sense to move this back outside of the "Repository development" chapter at some point since this is relevant in other contexts.

# -*- 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 entity's classes"""