docs: Add 'confval' object type to Sphinx

docs/conf.py

@@ -266,3 +266,12 @@ latex_documents = [
 needs_sphinx = '1.0'
 
 extlinks = {'issue': ('https://github.com/mopidy/mopidy/issues/%s', '#')}
+
+
+def setup(app):
+    from sphinx.ext.autodoc import cut_lines
+    app.connect(b'autodoc-process-docstring', cut_lines(4, what=['module']))
+    app.add_object_type(
+        b'confval', 'confval',
+        objname='configuration value',
+        indextemplate='pair: %s; configuration value')