Feature: Added post sharing options.

Also added a license statement at the bottom of the posts.

_includes/post-nav.html

@@ -0,0 +1,28 @@
+<!--
+  Navigation buttons at the bottom of the post.
+
+  v2.1
+  https://github.com/cotes2020/jekyll-theme-chirpy
+  © 2020 Cotes Chung
+  MIT License
+-->
+
+<div class="post-navigation d-flex justify-content-between">
+  {% if page.previous.url %}
+  <a href="{{ site.baseurl }}{{ page.previous.url }}" class="btn btn-outline-primary">
+    <p>{{ page.previous.title }}</p>
+  {% else %}
+  <a href="javascript:;" class="btn btn-outline-primary disabled">
+    <p>-</p>
+  {% endif %}
+  </a>
+
+  {% if page.next.url %}
+  <a href="{{ site.baseurl }}{{page.next.url}}" class="btn btn-outline-primary">
+    <p>{{ page.next.title }}</p>
+  {% else %}
+    <a href="javascript:;" class="btn btn-outline-primary disabled">
+    <p>-</p>
+  {% endif %}
+  </a>
+</div>

_includes/post-sharing.html

@@ -0,0 +1,28 @@
+<!--
+ Post sharing snippet
+
+ v2.1
+ https://github.com/cotes2020/jekyll-theme-chirpy
+ © 2019 Cotes Chung
+ Published under the MIT License
+-->
+
+<div class="share-wrapper">
+  <span class="share-label ml-1 mr-1">{{ site.data.share.label }}</span>
+  <span class="share-icon">
+    {% capture title %}{{ page.title }} - {{ site.title }}{% endcapture %}
+    {% assign url = page.url | relative_url | prepend: site.url %}
+
+    {% for share in site.data.share.platforms %}
+      {% assign link = share.link | replace: 'TITLE', title | replace: 'URL', url %}
+        <a href="{{ link }}" data-toggle="tooltip" data-placement="top"
+          title="{{ share.type }}" target="_blank">
+          <i class="fa-fw {{ share.icon }} mr-1"></i>
+        </a>
+    {% endfor %}
+
+    <i class="fa-fw fas fa-link mr-1 small" onclick="copyLink()"
+        data-toggle="tooltip" data-placement="top" title="Copy link"></i>
+
+  </span>
+</div>

_includes/related-posts.html

@@ -43,7 +43,7 @@
   {% assign score_list = score_list | sort | reverse %}
   {% assign count = 0 %}
   <div id="related-posts" class="mt-4 mb-2 mb-sm-4 pb-2">
-    <h3 class="pt-2 mt-1 mb-4" data-toc-skip>{{ site.data.label.post.relate_posts }}</h3>
+    <h3 class="pt-2 mt-1 mb-4 ml-1" data-toc-skip>{{ site.data.label.post.relate_posts }}</h3>
     <div class="card-deck mb-4">
     {% for score_item in score_list %}
       {% assign data = score_item | split: ":" %}