Merge pull request #3022 from canyon289/improve_dist_docstrings

Add docstrings to random and logp in continuous.py

Author: twiecki

docs/source/prob_dists.rst

@@ -30,7 +30,7 @@ All distributions in ``pm.distributions`` will have two important methods: ``ran
 
     class SomeDistribution(Continuous):
     
-        def random(self, point=None, size=None, repeat=None):
+        def random(self, point=None, size=None):
             ...
             return random_samples