get access to public methods of the hangups Client

the client methods can be accessed via ```bot._client.<method>``` and now also via ```bot.<method>```

If a method with the same name is implemented in the ```HangupsBot``` class, the method will be used instead.

e.x.:
calling ```bot._client.upload_image(<args>)``` is an access to a private member of ```bot```, however the method ```image_upload``` is a common method and an access should not violate any permission. It can be accessed now via ```bot.image_upload```.

hangupsbot/hangupsbot.py

@@ -608,6 +608,23 @@ def user_self(self):
 
         return myself
 
+    def __getattr__(self, attr):
+        """bridge base requests to the hangups client
+
+        Args:
+            attr: string, method name of hangups.client.Client
+
+        Returns:
+            callable, the requested method if it is not private
+
+        Raises:
+            NotImplementedError: the method is private or not implemented
+        """
+        if attr and attr[0] != "_" and hasattr(self._client, attr):
+            return getattr(self._client, attr)
+        raise NotImplementedError()
+
+
 def configure_logging(args):
     """Configure Logging