add chapter name display on pages

sass/style.scss

@@ -123,7 +123,7 @@ ul, ol {
     margin-bottom: 0.5rem;
   }
 
-  time {
+  time, .chapter {
     color: var(--muted);
     font-size: 0.9rem;
   }

templates/page.html

@@ -8,9 +8,7 @@
 <article>
     <header class="post-header">
         <h1>{{ page.title }}</h1>
-        {% if page.date %}
+{% if page.extra.chapter %}<span class="chapter">{{ page.extra.chapter }} | </span>{% endif %}{% if page.date %}<time datetime="{{ page.date }}">{{ page.date | date(format="%B %d, %Y") }}</time>{% endif %}
-        <time datetime="{{ page.date }}">{{ page.date | date(format="%B %d, %Y") }}</time>
-        {% endif %}
     </header>
     <div class="content">
         {% if page.content is containing("<!--TOC_PLACEHOLDER-->") %}