Add support for GitHub avatars to replace Gravatar (#36)

Author: ~hacker

README.md

@@ -69,6 +69,10 @@ dash:
       color: purple
 
   show_author: true
+
+# Replaces the default avatar provider (gravatar)
+#avatar_source: github
+#github_username: bitbrain
 ```
 ## Using this theme directly on Github Pages
 

_config.yml

@@ -46,3 +46,7 @@ plugins:
  - jekyll-paginate
  - liquid-md5
  - jekyll/tagging
+
+# Replaces the default avatar provider (gravatar)
+#avatar_source: github
+#github_username: bitbrain

_includes/author.html

@@ -1,6 +1,15 @@
 <div class="author-box">
-{% if site.plugins contains "liquid-md5" %}
-<img src="https://gravatar.com/avatar/{{ site.email | downcase | md5 }}?s=256" class="author-avatar" />
-{% endif %}
+    {% if site.avatar_source == "github" and site.github_username %}
+        {% capture avatar_image %}
+            https://github.com/{{ site.github_username }}.png
+        {% endcapture %}
+    {% elsif site.plugins contains "liquid-md5" %}
+        {% capture avatar_image %}
+            https://gravatar.com/avatar/{{ site.email | downcase | md5 }}?s=256
+        {% endcapture %}
+    {% endif %}
+    {% if avatar_image %}
+        <img src="{{ avatar_image }}" class="author-avatar" alt="Avatar" />
+    {% endif %}
 {{ site.description }}
 </div>