added thumbnail option (#1)
added thumbnail option (#1)

lightbox2 source has thumbs

          <h3 style="clear: both;">Four image set</h3>
          <div class="image-row">
            <div class="image-set">
              <a class="example-image-link" href="images/image-3.jpg" data-lightbox="example-set" data-title="Click the right half of the image to move forward."><img class="example-image" src="images/thumb-3.jpg" alt="Golden Gate Bridge with San Francisco in distance"></a>
              <a class="example-image-link" href="images/image-4.jpg" data-lightbox="example-set" data-title="Or press the right arrow on your keyboard."><img class="example-image" src="images/thumb-4.jpg" alt="Forest with mountains behind"></a>
              <a class="example-image-link" href="images/image-5.jpg" data-lightbox="example-set" data-title="The next image in the set is preloaded as you&apos;re viewing."><img class="example-image" src="images/thumb-5.jpg" alt="Bicyclist looking out over hill at ocean"></a>
              <a class="example-image-link" href="images/image-6.jpg" data-lightbox="example-set" data-title="Click anywhere outside the image or the X to the right to close."><img class="example-image" src="images/thumb-6.jpg" alt="Small lighthouse at bottom with ocean behind"></a>
            </div>
          </div>
appfoundry/jekyll-lightbox