Fix missing TOC in posts, add data-toc attribute

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

Author: troglobit

_layouts/post.html

@@ -12,7 +12,7 @@
 
 {% include lang.html %}
 
-<article class="px-1">
+<article class="px-1" data-toc="{{ page.toc }}">
   <header>
     <h1 data-toc-skip>{{ page.title }}</h1>
     {% if page.description %}