Dynamically retrieve version information for generated docs

Signed-off-by: Joffrey F <joffrey@docker.com>

docs/conf.py

@@ -69,10 +69,12 @@ author = u'Docker Inc'
 # |version| and |release|, also used in various other places throughout the
 # built documents.
 #
-# The short X.Y version.
-version = u'2.0'
+with open('../docker/version.py', 'r') as vfile:
+    exec(vfile.read())
 # The full version, including alpha/beta/rc tags.
-release = u'2.0'
+release = version
+# The short X.Y version.
+version = '{}.{}'.format(version_info[0], version_info[1])
 
 # The language for content autogenerated by Sphinx. Refer to documentation
 # for a list of supported languages.