Add remaining haskell book exercises

Haskell-book/15/orphan-instance/Listy.hs

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+module Listy where
+
+newtype Listy a =
+    Listy [a]
+    deriving (Eq, Show)
+
+instance Monoid (Listy a) where
+    mempty = Listy []
+    mappend (Listy l) (Listy l') =
+        Listy $ mappend l l'