Support '204 No Content' status code

Writing REST APIs often requires one end-point to return an empty response even if the client is expecting a JSON/XML object.

Instead of making the server return an explicit _empty_ object (e.g. ``{}``), a better solution is to send a '204 No Content' message back to the client.

On stackoverflow I found a small discussion on the subject: 
http://stackoverflow.com/questions/11970962/valid-json-in-response