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.params // => ['options']
Routes.users_path() // => "/users"
Routes.user_path // => "/users/:id(.:format)"
Routes.user_path.params // => ['_id', 'options']
Routes.user_path(1) // => "/users/1"
```
`options` parameter is something that we always support. As I understand you've designed that to return parameters passed to previous implementation of JS function. I think this is pretty useless. Lets return `['inbox_id', 'id']` instead and name it `required_params`. If people will want to see `options` there they will add it themselves.