Move related modules to Language.GraphQL.AST

Fixes #18.

- `Language.GraphQL.Encoder` moved to `Language.GraphQL.AST.Encoder`.
- `Language.GraphQL.Parser` moved to `Language.GraphQL.AST.Parser`.
- `Language.GraphQL.Lexer` moved to `Language.GraphQL.AST.Lexer`.
- All `Language.GraphQL.AST.Value` data constructor prefixes were removed. The
  module should be imported qualified.
- All `Language.GraphQL.AST.Core.Value` data constructor prefixes were removed.
  The module should be imported qualified.
- `Language.GraphQL.AST.Transform` is now isn't exposed publically anymore.

tests/Language/GraphQL/AST/ParserSpec.hs

@@ -0,0 +1,26 @@
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE QuasiQuotes #-}
+module Language.GraphQL.AST.ParserSpec
+    ( spec
+    ) where
+
+import Language.GraphQL.AST.Parser
+import Test.Hspec (Spec, describe, it)
+import Test.Hspec.Megaparsec (shouldSucceedOn)
+import Text.Megaparsec (parse)
+import Text.RawString.QQ (r)
+
+spec :: Spec
+spec = describe "Parser" $ do
+    it "accepts BOM header" $
+        parse document "" `shouldSucceedOn` "\xfeff{foo}"
+
+    it "accepts block strings as argument" $
+        parse document "" `shouldSucceedOn` [r|{
+              hello(text: """Argument""")
+            }|]
+
+    it "accepts strings as argument" $
+        parse document "" `shouldSucceedOn` [r|{
+              hello(text: "Argument")
+            }|]