Provide stable doc version by naming docs directory 0.9.x, e.g.

doc/gh-pages.py

@@ -85,6 +85,10 @@ if __name__ == '__main__':
     for l in setup_lines:
         if l.startswith('VERSION'):
             tag = l.split("'")[1]
+
+            # Rename to, e.g., 0.9.x
+            tag = '.'.join(tag.split('.')[:-1] + ['x'])
+
             break
 
     if "dev" in tag: