Add link underline for main body; add link icon

Links in the main body part are now underlined on mouse hover.
<a> tags in the article content are expanded by an icon from
FontAwesome.

Fixes #140

static/css/main.css

@@ -194,6 +194,14 @@
  	line-height: 1.7em;
  }
 
+main a:hover {
+        text-decoration: underline;
+}
+
+main article .fa, main article .fas {
+        font-size: 10pt;
+}
+
  article img {
  	display: block;
  	margin: 3em auto;

templates/posts/details.html.tera

@@ -36,7 +36,7 @@
         {% endif %}
     </div>
     <article>
-        {{ article.post.content | safe }}
+        {{ article.post.content | safe | replace(from="</a>", to=" <i class='fas fa-external-link-alt'></i></a>") }}
     </article>
 
     <div class="article-meta">