Show tagline only if set. credit to @sway as seen in pull emacs-jp#48

Author: plusjade

_includes/themes/twitter/page.html

@@ -1,5 +1,5 @@
 <div class="page-header">
-  <h1>{{ page.title }} <small>{{ page.tagline }}</small></h1>
+  <h1>{{ page.title }} {% if page.tagline %} <small>{{ page.tagline }}</small>{% endif %}</h1>
 </div>
 
 <div class="row">