add basic query struct, support 1.12

cmd/genql/main.go

@@ -0,0 +1,16 @@
+package main
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/Khan/genql/generate"
+)
+
+func main() {
+	err := generate.Generate()
+	if err != nil {
+		fmt.Println(fmt.Errorf("genql failed: %v", err))
+		os.Exit(1)
+	}
+}