docs: include Beaker version in title

Change-Id: I63c8abf9813694f4a5f09b3f5aaae9c1fdaae00f
docs: use new format for intersphinx_mapping config value

This format is new in Sphinx 1.0+. It lets us more easily override the
intersphinx mappings in beaker-project.org.

See: http://sphinx-doc.org/ext/intersphinx.html#confval-intersphinx_mapping

Change-Id: Ia9ac880e1a3e9e5b2c39751507a43d80800c938b