code: function load(rulesDir) {
    var newRules = loadRules(rulesDir);
    Object.keys(newRules).forEach(function(ruleId) {
      define(ruleId, newRules[ruleId]);
    });
  }
docs: Loads and registers all rules from passed rules directory.
  @param {String} [rulesDir] Path to rules directory, may be relative. Defaults to `lib/rules`.
  @returns {void}