Added automated jsonp support with validation based on the presence of
the 'callback' GET param;
Also works should:
* the requesting Content-Type is application/json instead of application/javascript;
* the format GET param is: json
* file extension: .json
Removed _format_jsonp which depends on file extension .jsonp or 'format' query param;
See #202: Consider removing the _format_ factory
Removed 5dd96ce (#202) following 58955e5 (fix #244);
Merge pull request #259 from chernjie/master

Improved support for jsonp callbacks