Create short link

This method creates a new link. If parameter "path" is omitted, it
generates path by algorithm, chosen in domain settings.

Notes:

1. If URL with a given path already exists and originalURL of the URL in database is equal to originalURL argument, it returns information about existing URL
2. If URL with a given path already exists and originalURL is different from originalURL in database, it returns error with a status 409
3. If URL with a given originalURL exists, and no path is given, it returns information about existing URL and does not create anything
4. If URL with a given originalURL exists, and custom path is given, it creates a new short URL

Rate limit: 20/s