Routes path specs

Based by #123 , but here we don't have separate function `spec` to get spec of route. We override `toString` for route function, and this give for us to get function spec in this way:

```js
Routes.users_path // => "/users(.:format)"
Routes.users_path.required_params // => []
Routes.users_path() // => "/users"
Routes.user_path // => "/users/:id(.:format)"
Routes.user_path.required_params // => ['id']
Routes.user_path(1) // => "/users/1"
```
It will be hard to guess the required parameters based on currently generated code:

``` js
inbox_message_path: Utils.route(["inbox_id", "id"], "inbox_id", "id", ....)
```

If we can not make it clear than lets make an extra line of comments that shows the correct function signature, like:

``` js
// function(inbox_id, id, options)
```