Mention platinum sponsors in footer.

pinaxcon/templates/_footer.html

@@ -1,4 +1,5 @@
 {% load staticfiles %}
+{% load sponsorship_tags %}
 <div class="row">
 
   <div class="logo">
@@ -10,6 +11,16 @@
   <div class="footer-copy">
     <p>&copy; 2017 North Bay Python, member project of <a href="https://sfconservancy.org" >Software Freedom Conservancy</a>, a 501(c)(3) charity.</p>
 
+    {% sponsors "platinum" as platinum %}
+
+    <p>We acknowledge the support of our Platinum sponsor{{ platinum|length|pluralize}},
+      {% for sponsor in platinum %}
+        {% if forloop.last and not forloop.first %}
+          and
+        {% endif %}
+        {{ sponsor }}{% if forloop.last %}.{% endif %}
+      {% endfor %}
+
     <p>
       <a href="https://facebook.com/northbaypython">Facebook</a>
       | <a href="https://twitter.com/northbaypython">Twitter</a>