add __dir__ implementation for SingleGroupApproximations (#3076)

* add __dir__ implementation for SingleGroupApproximations

This adds nice autocomplition properties and makes life easier

* increment release notes

Author: ferrine

RELEASE-NOTES.md

@@ -26,6 +26,7 @@
 - Add `model_to_graphviz` (which uses the optional dependency `graphviz`) to
   plot a directed graph of a PyMC3 model using plate notation.
 - Add beta-ELBO variational inference as in beta-VAE model (Christopher P. Burgess et al. NIPS, 2017)
+- Add `__dir__` to `SingleGroupApproximation` to improve autocompletion in interactive environments
 
 ### Fixes
 

pymc3/variational/approximations.py

@@ -539,6 +539,11 @@ def __init__(self, *args, **kwargs):
     def __getattr__(self, item):
         return getattr(self.groups[0], item)
 
+    def __dir__(self):
+        d = set(super(SingleGroupApproximation, self).__dir__())
+        d.update(self.groups[0].__dir__())
+        return list(sorted(d))
+
 
 class MeanField(SingleGroupApproximation):
     __doc__ = """**Single Group Mean Field Approximation**