Introduce graphql function

This simplifies Attoparsec parsing when executing a GraphQL
query.

Data/GraphQL.hs

@@ -0,0 +1,16 @@
+module Data.GraphQL where
+
+import Control.Applicative (Alternative, empty)
+
+import Data.Text (Text)
+
+import qualified Data.Aeson as Aeson
+import qualified Data.Attoparsec.Text as Attoparsec
+
+import Data.GraphQL.Execute
+import Data.GraphQL.Parser
+import Data.GraphQL.Schema
+
+graphql :: (Alternative m, Monad m) => Schema m -> Text -> m Aeson.Value
+graphql schema = either (const empty) (execute schema)
+               . Attoparsec.parseOnly document