render/func.go
func Func(s string, fn RendererFunc) Renderer {
	return funcRenderer{
		contentType: s,
		renderFunc:  fn,
	}
}
func Func(s string, fn RendererFunc) Renderer {
	return funcRenderer{
		contentType: s,
		renderFunc:  fn,
	}
}
// Func renderer allows for easily building one of renderers
// using just a RendererFunc and not having to build a whole
// implementation of the Render interface.