Move footer content into template

This caused problems because liquid >=3.0.0 does not allow a
variable and a template with the same name. Here we had a
variable and a template both called footer.

docs/templates/shared/_footer.liquid

@@ -1,6 +1,7 @@
     <footer>
       <div class="container">
-        {{ footer | markdownify }}
+        <p>This website is made with <a href="http://www.tinytree.info">Bonsai</a> and <a href="http://getbootstrap.com">Bootstrap</a>, themed with <a href="https://bootswatch.com">Bootswatch</a>.</p>
+        <p>jq is licensed under the MIT license (code) and the <a href="https://creativecommons.org/licenses/by/3.0/">CC-BY-3.0</a> license (docs).</p>
       </div>
     </footer>