add valid() to parameters

Author: anxdpanic

resources/lib/twitch/api/parameters.py

@@ -5,6 +5,10 @@
 class _Parameter(object):
     _valid = []
 
+    @classmethod
+    def valid(cls):
+        return cls._valid
+
     @classmethod
     def validate(cls, value):
         if value in cls._valid: