Feature: isin

Added the method isin following the example of other methods that get delegated to pandas. Not sure (yet), if I am missing something, so I guess you should merge @palmb

dios/dios.py

@@ -641,6 +641,10 @@ class DictOfSeries:
         else:
             return DictOfSeries(data=data, itype=self.itype, cast_policy=self._policy, fastpath=True)
 
+    def isin(self, values):
+        data = self._fast_apply('isin', values=values)
+        return DictOfSeries(data=data, itype=self.itype, cast_policy=self._policy, fastpath=True)
+
     def memory_usage(self, index=True, deep=False):
         mem = 0
         for k in self.columns: