Integrate support for logging for multiple log levels

[addityasingh]

As: A user of this package,
I would want: My server to have an option to log events

E.g. In below example we allow the server to log all the logs with info and error

var options = {
    key: fs.readFileSync(__dirname + '/keys/spdy-key.pem'),
    cert: fs.readFileSync(__dirname + '/keys/spdy-fullchain.pem'),
    debug: { 
        request: ['error', 'info'] 
    } 
}
var server = spdy.createServer(options, function(req, res) {
  res.writeHead(200);
  res.end('hello world!');
});