Validate urls with spaces

[goganchic]

I use such example:

# API name

## Group Users

### Users [GET /hello world]

+ Response 200

I expect to receive a warning or an error about space in url /hello world because url should not contain any spaces, but drafter considers example as correct one.

[goganchic]

https://github.com/apiaryio/drafter/blob/master/test/fixtures/syntax/undisclosed-listitem.apib in this test whole string / GET recognized as url, but as I understand only / is url.