feat(helper): introduce factory helper

[yusukebe]

This PR introduces factory helper. Now, this provides a middleware factory method to create a middleware handler.

const mw = (message: string) =>
  middleware(async (c, next) => {
    await next()
    c.header('X-Message', message)
  })

If define your middleware with middleware, the appropriate types will be added.

Author should do the followings, if applicable

• Add tests
• Run tests
• yarn denoify to generate files for Deno