Add Eq and Show instances to SumBag

This is a requirement for its use in copar and also allows for testing, since
`shouldBe` from hspec requires those two instances.

src/Data/SumBag.hs

@@ -16,6 +16,10 @@ import qualified Data.List.NonEmpty as NE
 type SumBag a = Tree a
 
 data Tree a = Leaf | Node (MetaData a) (Element a) (Tree a) (Tree a)
+  deriving (Show)
+
+instance (Ord a, Eq a) => Eq (Tree a) where
+  x == y = toAscList x == toAscList y
 
 type role Tree nominal
 
@@ -23,11 +27,13 @@ data MetaData a = MetaData
   { nodeSize :: Int
   , nodeSum :: a
   }
+  deriving (Show)
 
 data Element a = Element
   { value :: a
   , multiplicity :: NE.NonEmpty a
   }
+  deriving (Show)
 
 
 empty :: SumBag a