code: function getWriteFunction(log) {
    return function writeLogFile (name, qcb) {
      var dir = path.join(LOG_DIR, name);
  
      function readFile (cb) {
        fs.readFile(dir, cb);
      }
  
      function updateLogs (logs, cb) {
        logs.push(log.toJSON());
        cb(null, logs);
      }
  
      function writeFile (str, cb) {
        fs.writeFile(dir, str, cb);
      }
  
      async.waterfall([
        readFile,
        safejson.parse,
        updateLogs,
        safejson.stringify,
        writeFile
      ], qcb);
    };
  }
docs: Generates a function that will perform logic required
  to update a log file with a new log entry.
  @param  {Log} log [description]