added and implemented epsilon_greedy.py

Author: bing-j

axelrod/strategies/epsilon_greedy.py

@@ -13,7 +13,7 @@ class EpsilonGreedy(Player):
 
     Names:
 
-    # TODO: reference Sutton & Barto's Reinforcement Learning: an Introduction
+    # TODO: reference Sutton & Barto's Reinforcement Learning: an Introduction 2nd Ed.
     """
 
     name = "$\varepsilon$-greedy"