basic support for fragments

generate/testdata/SimpleFragment.graphql

@@ -0,0 +1,11 @@
+fragment profileData on User {
+  name
+  emails
+}
+
+query {
+  user {
+    id
+    ...profileData
+  }
+}

generate/testdata/SimpleFragment.graphql.go

@@ -0,0 +1,11 @@
+type ProfileData struct {
+	Name   *string  `json:"name"`
+	Emails []string `json:"emails"`
+}
+
+type Response struct {
+	User *struct {
+		Id string `json:"id"`
+		ProfileData
+	} `json:"user"`
+}