Add optional email address to author bio and feed.xml

- Fixes #35
- To add additional social network profiles edit _author-bio.html
- Icons come from the Font Awesome webfont. See http://fontawesome.io/icons/ for a complete list

_includes/_author-bio.html

@@ -9,6 +9,7 @@
 {% endif %}
 <h3>{{ author.name }}</h3>
 <p>{{ author.bio }}</p>
+{% if author.email %}<a href="mailto:{{ author.email }}" class="author-social" target="_blank"><i class="fa fa-envelope-square"></i> {{ author.email }}</a>{% endif %}
 {% if author.twitter %}<a href="http://twitter.com/{{ author.twitter }}" class="author-social" target="_blank"><i class="fa fa-twitter-square"></i> Twitter</a>{% endif %}
 {% if author.facebook %}<a href="http://facebook.com/{{ author.facebook }}" class="author-social" target="_blank"><i class="fa fa-facebook-square"></i> Facebook</a>{% endif %}
 {% if author.google_plus %}<a href="http://plus.google.com/+{{ author.google_plus }}" class="author-social" target="_blank"><i class="fa fa-google-plus-square"></i> Google+</a>{% endif %}

feed.xml

@@ -13,7 +13,7 @@ sitemap: false
 <author>
   <name>{{ site.owner.name }}</name>
   <uri>{{ site.url }}/</uri>
-  <email>{{ site.owner.email }}</email>
+  {% if site.owner.email %}<email>{{ site.owner.email }}</email>{% endif %}
 </author>
 {% for post in site.posts limit:20 %}