Add ToSample instances for (), Bool and Ordering

Also remove `instance ToSample ()` from example.

servant-docs/example/greet.hs

@@ -53,9 +53,6 @@ instance ToParam (MatrixParam "lang" String) where
                   "Get the greeting message selected language. Default is en."
                   Normal
 
-instance ToSample () () where
-  toSample _ = Just ()
-
 instance ToSample Greet Greet where
   toSample _ = Just $ Greet "Hello, haskeller!"
 

servant-docs/src/Servant/Docs/Internal.hs

@@ -961,6 +961,11 @@ instance HasDocs sublayout => HasDocs (Vault :> sublayout) where
   docsFor Proxy ep =
     docsFor (Proxy :: Proxy sublayout) ep
 
+-- 'ToSample' instances for simple types
+
+instance ToSample () ()
+instance ToSample Bool Bool
+instance ToSample Ordering Ordering
 
 -- polymorphic 'ToSample' instances