code: function digestFile(file, algorithm, encoding) {
      return crypto.createHash(algorithm || 'md5').update(fs.readFileSync(file)).digest(encoding || 'hex');
  }
docs: digest file content.
  
  @param {String} file
  @param {String} [algorithm='md5']  'sha1', 'md5', 'sha256', 'sha512'...
  @param {String} [encoding='hex'] 'hex', 'binary' or 'base64'
  @return {String} digest string