total rewrite to interface handling; not complete but it compiles

generate/testdata/SimpleQuery.graphql.go

@@ -1,5 +1,29 @@
-type Response struct {
-	User *struct {
-		Id string `json:"id"`
-	} `json:"user"`
+package test
+
+// Code generated by github.com/Khan/genql, DO NOT EDIT.
+
+import (
+	"context"
+
+	"github.com/Khan/genql/graphql"
+)
+
+type SimpleQueryResponse struct {
+	User *User `json:"user"`
+}
+
+type User struct {
+	Id string `json:"id"`
+}
+
+func SimpleQuery(client *graphql.Client) (*SimpleQueryResponse, error) {
+	var retval SimpleQueryResponse
+	err := client.MakeRequest(context.Background(), `
+query SimpleQuery {
+	user {
+		id
+	}
+}
+`, &retval, nil)
+	return &retval, err
 }