refactor: Add doctests

test/doctests/Main.hs

@@ -0,0 +1,17 @@
+module Main (main) where
+
+import Test.DocTest (doctest)
+
+import Protolude
+
+
+main :: IO ()
+main =
+  doctest
+    [ "--verbose"
+    , "-XOverloadedStrings"
+    , "-XNoImplicitPrelude"
+    , "-XStandaloneDeriving"
+    , "-isrc"
+    , "src/PostgREST/Request/Preferences.hs"
+    ]