Adding a preProcess config option

This is a small feature which lets you manipulate the log with a custom function before its pushed out.

We've used it like this : 

    manifest.plugins['hapi-bunyan-lite'] = {
      logger: myRootLogger,
      defaultLogLevel: 'trace',
      preProcessData: function preProcessData(objLog, event, tags, request) {

        if (typeof event.data === 'string') {
          event.data = {
            msg: event.data
          };
        };

        if (request) {
          objLog.remoteAddress = request.remoteAddress;
          objLog.host = request.host;
          objLog.path = request.path;
          objLog.method = request.method;
          objLog.received = request.info.received;
          objLog.msec = new Date().getTime() - request.info.received;
          objLog.isAuthenticated = request.auth.isAuthenticated
        }
        
      }
    };

Which makes the logs a joy to work with in http://www.elasticsearch.org/overview/kibana/ and lets us trace down bottle necks.