add standardization shaper

src/pymgrid/microgrid/reward_shaping/standardization_shaper.py

@@ -0,0 +1,13 @@
+from pymgrid.microgrid.reward_shaping.base import BaseRewardShaper
+from pymgrid.utils.running_mean_std import RunningMeanStd
+
+
+class StandardizationShaper(BaseRewardShaper):
+    yaml_tag = u'StandardizationShaper'
+
+    def __init__(self):
+        self.reward_running_mean_std = RunningMeanStd()
+
+    def __call__(self, original_reward, step_info, cost_info):
+        self.reward_running_mean_std.update(original_reward)
+        return (original_reward - self.reward_running_mean_std.mean) / self.reward_running_mean_std.var