code: function Setting(settingSpec, settings) {
      this._settings = settings;
  
      Object.keys(settingSpec).forEach(function(key) {
          this[key] = settingSpec[key];
      }, this);
  
      this.type = types.getType(this.type);
      if (this.type == null) {
          throw new Error('In ' + this.name +
              ': can\'t find type for: ' + JSON.stringify(settingSpec.type));
      }
  
      if (!this.name) {
          throw new Error('Setting.name == undefined. Ignoring.', this);
      }
  
      if (!this.defaultValue === undefined) {
          throw new Error('Setting.defaultValue == undefined', this);
      }
  
      if (this.onChange) {
          this.on('change', this.onChange.bind(this))
      }
  
      this.set(this.defaultValue);
  }
docs: Create a new setting.
  @param settingSpec An object literal that looks like this:
  {
  name: 'thing',
  description: 'Thing is an example setting',
  type: 'string',
  defaultValue: 'something'
  }