code: function make (options) {
      var shopifyTheme;
      var previous = shopifyThemeInstances.filter((instance)=>{
          return options.shop_name === instance._shopName && options.api_key === instance._apiKey;
      });
      if (previous.length) return previous[0];
      shopifyTheme = new ShopifyTheme( options );
      shopifyThemeInstances.push(shopifyTheme);
      return shopifyTheme;
  }
docs: /*
  var theme = shopifytheme.create();
  gulp.src().pipe(theme.stream());
  theme.init(options);