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"
```
I've implemented `_` as a prefix for parameter name for the case of collision with javascript reserved word. Ex. `/returns/:return` - JS function generated from this route using previous implementation required the underscore otherwise JS would not complile `function(return, options) {}` because of reserved name `return`.

I think this solution is not required now at all and params should return `id` without underscore.