README: Add Router#url() query params support description and examples

Author: wachunei

README.md

@@ -32,7 +32,7 @@ npm install koa-router
 ```
 
 ## API Reference
-  
+
 * [koa-router](#module_koa-router)
     * [Router](#exp_module_koa-router--Router) ⏏
         * [new Router([opts])](#new_module_koa-router--Router_new)
@@ -44,7 +44,7 @@ npm install koa-router
             * [.allowedMethods([options])](#module_koa-router--Router+allowedMethods) ⇒ <code>function</code>
             * [.redirect(source, destination, code)](#module_koa-router--Router+redirect) ⇒ <code>Router</code>
             * [.route(name)](#module_koa-router--Router+route) ⇒ <code>Layer</code> &#124; <code>false</code>
-            * [.url(name, params)](#module_koa-router--Router+url) ⇒ <code>String</code> &#124; <code>Error</code>
+            * [.url(name, params [, options])](#module_koa-router--Router+url) ⇒ <code>String</code> &#124; <code>Error</code>
             * [.param(param, middleware)](#module_koa-router--Router+param) ⇒ <code>Router</code>
         * _static_
             * [.url(path, params)](#module_koa-router--Router.url) ⇒ <code>String</code>
@@ -224,9 +224,9 @@ sequentially, requests start at the first middleware and work their way
 
 | Param | Type |
 | --- | --- |
-| [path] | <code>String</code> | 
-| middleware | <code>function</code> | 
-| [...] | <code>function</code> | 
+| [path] | <code>String</code> |
+| middleware | <code>function</code> |
+| [...] | <code>function</code> |
 
 **Example**  
 ```javascript
@@ -252,7 +252,7 @@ Set the path prefix for a Router instance that was already initialized.
 
 | Param | Type |
 | --- | --- |
-| prefix | <code>String</code> | 
+| prefix | <code>String</code> |
 
 **Example**  
 ```javascript
@@ -340,11 +340,11 @@ Lookup route with given `name`.
 
 | Param | Type |
 | --- | --- |
-| name | <code>String</code> | 
+| name | <code>String</code> |
 
 <a name="module_koa-router--Router+url"></a>
 
-#### router.url(name, params) ⇒ <code>String</code> &#124; <code>Error</code>
+#### router.url(name, params [, options]) ⇒ <code>String</code> &#124; <code>Error</code>
 Generate URL for route. Takes a route name and map of named `params`.
 
 **Kind**: instance method of <code>[Router](#exp_module_koa-router--Router)</code>  
@@ -353,7 +353,8 @@ Generate URL for route. Takes a route name and map of named `params`.
 | --- | --- | --- |
 | name | <code>String</code> | route name |
 | params | <code>Object</code> | url parameters |
-
+| [options] | <code>Object</code> | options parameter |
+| [options.query] | <code>Object</code> &#124; <code>String</code> | query options |
 **Example**  
 ```javascript
 router.get('user', '/users/:id', function (ctx, next) {
@@ -366,6 +367,12 @@ router.url('user', 3);
 router.url('user', { id: 3 });
 // => "/users/3"
 
+router.url('user', { id: 3 }, { query: { limit: 1 } });
+// => "/users/3?limit=1"
+
+router.url('user', { id: 3 }, { query: "limit=1" });
+// => "/users/3?limit=1"
+
 router.use(function (ctx, next) {
   // redirect to named route
   ctx.redirect(ctx.router.url('sign-in'));
@@ -381,8 +388,8 @@ validation.
 
 | Param | Type |
 | --- | --- |
-| param | <code>String</code> | 
-| middleware | <code>function</code> | 
+| param | <code>String</code> |
+| middleware | <code>function</code> |
 
 **Example**  
 ```javascript