Add setup to module import

This allows us to configure the extension as 'zuul_sphinx' rather
than 'zuul_sphinx.zuul'.

Change-Id: I8a1534f7c2614ee11411cf228de38931257fc970

zuul_sphinx/__init__.py

@@ -0,0 +1,15 @@
+# Copyright 2017 Red Hat, Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License"); you may
+# not use this file except in compliance with the License. You may obtain
+# a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+# License for the specific language governing permissions and limitations
+# under the License.
+
+from zuul_sphinx.zuul import setup