*
* Match URL patterns to callback functions or controller actions using `router.verb()`,
* where **verb** is one of the HTTP verbs such as `router.get()` or `router.post()`.
*
* Additionaly, `router.all()` can be used to match against all methods.
*
* ```javascript
* router
* .get('/', (ctx, next) => {
* ctx.body = 'Hello World!';
* })
* .post('/users', (ctx, next) => {
* // ...
* })
* .put('/users/:id', (ctx, next) => {
* // ...
* })
* .del('/users/:id', (ctx, next) => {
* // ...
* })
* .all('/users/:id', (ctx, next) => {
* // ...
* });
* ```
*
* When a route is matched, its path is available at `ctx._matchedRoute` and if named,
* the name is available at `ctx._matchedRouteName`
*
* Route paths will be translated to regular expressions using
* [path-to-regexp](https://github.com/pillarjs/path-to-regexp).
*
* Query strings will not be considered when matching requests.
*
* #### Named routes
*
* Routes can optionally have names. This allows generation of URLs and easy
* renaming of URLs during development.
*
* ```javascript
* router.get('user', '/users/:id', (ctx, next) => {
* // ...
* });
*
* router.url('user', 3);
* // => "/users/3"
* ```
*
* #### Multiple middleware
*
* Multiple middleware may be given:
*
* ```javascript
* router.get(
* '/users/:id',
* (ctx, next) => {
* return User.findOne(ctx.params.id).then(function(user) {
* ctx.user = user;
* next();
* });
* },
* ctx => {
* console.log(ctx.user);
* // => { id: 17, name: "Alex" }
* }
* );
* ```
*
* ### Nested routers
*
* Nesting routers is supported:
*
* ```javascript
* var forums = new Router();
* var posts = new Router();
*
* posts.get('/', (ctx, next) => {...});
* posts.get('/:pid', (ctx, next) => {...});
* forums.use('/forums/:fid/posts', posts.routes(), posts.allowedMethods());
*
* // responds to "/forums/123/posts" and "/forums/123/posts/123"
* app.use(forums.routes());
* ```
*
* #### Router prefixes
*
* Route paths can be prefixed at the router level:
*
* ```javascript
* var router = new Router({
* prefix: '/users'
* });
*
* router.get('/', ...); // responds to "/users"
* router.get('/:id', ...); // responds to "/users/:id"
* ```
*
* #### URL parameters
*
* Named route parameters are captured and added to `ctx.params`.
*
* ```javascript
* router.get('/:category/:title', (ctx, next) => {
* console.log(ctx.params);
* // => { category: 'programming', title: 'how-to-node' }
