Add GitHub fork and star buttons to footer.

Directly borrowed from the Bootstrap docs again.

docs/_includes/footer.html

@@ -1,5 +1,6 @@
 <footer class="s2-docs-footer" role="contentinfo">
   <div class="container">
+    {% include social-buttons.html %}
     <p>
       Select2 is licensed under <a href="https://github.com/select2/select2/blob/master/LICENSE.md">MIT</a>, documentation under <a href="https://creativecommons.org/licenses/by/3.0/">CC BY 3.0</a>.
     </p>

docs/_includes/social-buttons.html

@@ -0,0 +1,10 @@
+<div class="s2-docs-social">
+  <ul class="s2-docs-social-buttons">
+    <li>
+      <iframe class="github-btn" src="http://ghbtns.com/github-btn.html?user=select2&amp;repo=select2&amp;type=watch&amp;count=true" width="100" height="20" title="Star on GitHub"></iframe>
+    </li>
+    <li>
+      <iframe class="github-btn" src="http://ghbtns.com/github-btn.html?user=select2&amp;repo=select2&amp;type=fork&amp;count=true" width="102" height="20" title="Fork on GitHub"></iframe>
+    </li>
+  </ul>
+</div>

docs/_sass/_s2-docs-social.scss

@@ -0,0 +1,32 @@
+/*
+ * Social buttons
+ *
+ * Twitter and GitHub social action buttons (for homepage and footer).
+ */
+
+.s2-docs-social {
+  margin-bottom: 20px;
+  text-align: center;
+}
+.s2-docs-social-buttons {
+  display: inline-block;
+  padding-left: 0;
+  margin-bottom: 0;
+  list-style: none;
+}
+.s2-docs-social-buttons li {
+  display: inline-block;
+  padding: 5px 8px;
+  line-height: 1;
+}
+.s2-docs-social-buttons .twitter-follow-button {
+  width: 225px !important;
+}
+.s2-docs-social-buttons .twitter-share-button {
+  width: 98px !important;
+}
+/* Style the GitHub buttons via CSS instead of inline attributes */
+.github-btn {
+  overflow: hidden;
+  border: 0;
+}

docs/css/s2-docs.scss

@@ -9,6 +9,7 @@
 @import "s2-docs-alert";
 @import "s2-docs-home";
 @import "s2-docs-examples";
+@import "s2-docs-social";
 @import "anchorjs";
 @import "jumbotron";
 @import "prettify";