Add 'section' utility

[CodeLenny]

Better name than section()?

  /**
   * Produces an array containing one or more configurable sections.
   * @param {String|String[]} setting the desired section(s) of output to include.  `null` or `undefined` to include all
   *   possible options.
   * @param {Any[]} options possible sections to include in output.
   * @return {Array<Any>} the items from the desired section(s)
   * @example <caption>Usage with JSVerify</caption>
   * static nameGenerator(setting) {
   *   return jsc.oneof(this.ensureGenerator(this.section(setting, {
   *     communicators: [ "bob", "jane", "carlos", "frank" ],
   *     attackers: [ "craig", "eve", "mallory", "sybil" ],
   *     government: "grace",
   *     aid: [ "faythe", "trent", "victor", "walter" ],
   *   })));
   * }
   *
   * jsc.forall(nameGenerator(null), person => isPerson(person));
   * jsc.forall(nameGenerator("attackers"), person => isAttacker(person));
   * jsc.forall(nameGenerator([ "communicators", "aid" ]), person => isSafe(person));
   * jsc.forall(nameGenerator([ "attackers", "government" ]), person => !trustworthy(person));
  */
  static section(setting, options) {
    if(setting !== null || setting === undefined) {
      options = filter(options, (val, key) => Array.isArray(setting) ? setting.indexOf(key) > -1 : key === setting);
    }
    return union(map(options, (val) => Array.isArray(val) ? val : [ val ]));
  }