docs: function getChecksum(fs, path, callback) {
    fs.readFile(path, function(err, data) {
      if(!err) {
        callback(null, md5sum(data));
      } else if(err.code === 'ENOENT') {
        // File does not exist so the checksum is an empty string
        callback(null, "");
      } else {
        callback(err);
      }
    });
  }