xslate.go
func (tx *Xslate) RenderInto(w io.Writer, template string, vars Vars) error {
	bc, err := tx.Loader.Load(template)
	if err != nil {
		return err
	}
	tx.VM.Run(bc, vm.Vars(vars), w)
	return nil
}
func (tx *Xslate) RenderInto(w io.Writer, template string, vars Vars) error {
	bc, err := tx.Loader.Load(template)
	if err != nil {
		return err
	}
	tx.VM.Run(bc, vm.Vars(vars), w)
	return nil
}
// RenderInto combines Render() and writing its results into an io.Writer.
// This is a convenience method for frameworks providing a Writer interface,
// such as net/http's ServeHTTP()