Add support for post excerpts

Author: rcvalle

_config.yml

@@ -1,4 +1,5 @@
 baseurl: /jekyll-theme-bootstrap4
+excerpts: true
 exclude:
   - "*.gemspec"
   - "CONTRIBUTING*"

_includes/post.html

@@ -2,7 +2,12 @@
   <h1 itemprop="headline"><a href="{{ include.post.url | relative_url }}">{{ include.post.title }}</a></h1>
   <p>{% if include.post.author %}By <span itemprop="author">{{ include.post.author }}</span> on {% endif %}<time itemprop="datePublished" datetime="{{ include.post.date | date_to_xmlschema }}">{{ include.post.date | date: "%B %-d, %Y" }}</time>{% if include.post.comments %}. <a href="{{ include.post.url | relative_url }}#disqus_thread" data-disqus-identifier="{{ include.post.url | relative_url }}"></a>{% endif %}</p>
   <div itemprop="articleBody">
-    {{ include.post.content | markdownify }}
+    {% if page.type == "home" and site.excerpts %}
+      {{ include.post.excerpt | markdownify }}
+      <p><a href="{{ post.url }}">Read more&hellip;</a></p>
+    {% else %}
+      {{ include.post.content | markdownify }}
+    {% endif %}
   </div>
   <p>{% include post_tags.html post=include.post %}</p>
 </article>