initialize Winston logging mechanism from file
function fromFile(filename, callback) {
  var configFile = filename || '../config/winston-config.json';

  fs.exists(configFile, function (exists) {
    if (exists) {
      var winstonConf = require(configFile).logging;

      fromJson(winstonConf, callback);
    } else {
      callback(new Error('No config file found (at least provide a config/winston-config.json) with winston configuration'), winston);
    }
  });
}