Add defaults to icons

Author: gaelicWizard

_includes/icons.html

@@ -1,6 +1,6 @@
-{% if site.social.email %}
+{% if site.social.email or site.email %}
 <li>
-  <a href="mailto:{{ site.author.email }}" title="email">
+  <a href="mailto:{{ site.author.email | default: site.email }}" title="email">
     <span class="fa-stack fa-lg">
       <i class="fa fa-circle fa-stack-2x"></i>
       <i class="fa fa-envelope fa-stack-1x fa-inverse"></i>
@@ -64,9 +64,9 @@
 </li>
 {% endif %}
 
-{% if site.social.github %}
+{% if site.social.github or site.github_username %}
 <li>
-  <a href="https://github.com/{{ site.social.github }}" title="{{ site.social.default_txt }} GitHub">
+  <a href="https://github.com/{{ site.social.github | default: site.github_username }}" title="{{ site.social.default_txt }} GitHub">
     <span class="fa-stack fa-lg">
       <i class="fa fa-circle fa-stack-2x"></i>
       <i class="fab fa-github fa-stack-1x fa-inverse"></i>
@@ -196,9 +196,9 @@
 </li>
 {% endif %}
 
-{% if site.social.twitter %}
+{% if site.social.twitter or site.twitter_username %}
 <li>
-  <a href="https://twitter.com/{{ site.social.twitter }}" title="{{ site.social.default_txt }} Twitter" class="type">
+  <a href="https://twitter.com/{{ site.social.twitter | default: site.twitter_username }}" title="{{ site.social.default_txt }} Twitter" class="type">
     <span class="fa-stack fa-lg">
       <i class="fa fa-circle fa-stack-2x"></i>
       <i class="fab fa-twitter fa-stack-1x fa-inverse"></i>