Export getFieldOptional (.??) from Data.Argonaut.Decode.

Fixes #33.

Author: cdepillabout

src/Data/Argonaut/Decode.purs

@@ -4,4 +4,4 @@ module Data.Argonaut.Decode
   ) where
 
 import Data.Argonaut.Decode.Class (class DecodeJson, decodeJson)
-import Data.Argonaut.Decode.Combinators (getField, (.?))
+import Data.Argonaut.Decode.Combinators (getField, (.?), getFieldOptional, (.??))