Added `in-stock` keyword to tagged_with block

Added the in-stock keyword to tagged_with. If used, only products that are in stock will be shown in the tagged_with block.

{% tagged_with 'Hot Seller' do products in-stock %}
  <table border="0" class="invisible-table" width="100%">
    {% include 'product' with products %}
  </table>
{% endtagged_with %}