Add support for middleware to routes

[lindsaykwardell]

Support is required for middleware on routes. One use case is for authentication/authorization.

Potential example API:

Middleware applied to Router class object.

const router = new Router("/api");

router.use((req: ServerRequest): boolean => {
  // Perform middleware action
  // Return true if valid, false if the request should be interrupted.

  return true;
});

Middleware applied when adding routes to Server

const someMiddleware2 = (req: ServerRequest): boolean => {
  return true;
}

const app = new Server();

app.use(router.routes, (req: ServerRequest): boolean => {...}, someMiddleware2);