Add CORS headers

Added support for serving CORS headers using the connect-cors package.
Example headers

`
Access-Control-Allow-Origin: http://example.com
Access-Control-Allow-Headers: X-Requested-With, X-HTTP-Method-Override, Content-Type, Accept
Access-Control-Expose-Headers: X-Requested-With, X-HTTP-Method-Override, Content-Type, Accept
Access-Control-Allow-Methods: HEAD, GET, POST
`