<a href="http://twitter.com/barrkmadley/">twitter</a>
<a href="http://github.com/barkmadley/">github</a>
<a href="{{ site.baseurl }}/about/">about</a>
<a href="{{ site.baseurl }}/contact/">contact</a>

{% if site.twitter_username %}
<a href="http://twitter.com/{{site.twitter_username}}/">twitter</a>
{% endif %}
{% if site.github_username %}
<a href="http://github.com/{{site.github_username}}/">github</a>
{% endif %}
<a href="{{ site.baseurl }}/about/">about</a>
<a href="{{ site.baseurl }}/contact/">contact</a>

Make the nav links optional
Make the nav links optional
