code: function rule(test, loaders, exclude) {
      var rule = {
          test: test,
          use: loaders
      };
  
      if (exclude) {
          rule.exclude = exclude;
      }
  
      return rule;
  }
docs: Constructs a rule object.
  
  @param {RegEx} test The regular expression to use when testing a file path name.
  @param {Array} loaders The list of loaders to run the file through if it matches the test regex.
  @param {RegEx} exclude The regular express to use when excluding specific files that match the test regex.