[Feature] Staticman v3 Support (#440)

* Added Staicman support

* Corrected template for staticman.yml

* Edit for coherence with _includes/disqus.html

* Updated documentation for Staticman

* Updated License to give credits to Michale Rose

* Update LICENSE

* add more staticman details to readme

* Clearer instructions about reCAPTCHA in YML

* Nest reCAPTCHA param inside Staticman

* Prepend all css selectors with .staticman-comments

Edit suggested by theme owner to avoid CSS rules overriding.

* Add myself to the change log

* Update _config.yml

_includes/staticman-comment.html

@@ -0,0 +1,22 @@
+<article id="comment{{ include.index }}" class="js-comment comment" itemprop="comment" itemscope itemtype="https://schema.org/Comment">
+  <div class="comment__avatar-wrapper">
+    <img class="comment__avatar" src="https://www.gravatar.com/avatar/{{ include.email }}?d=mm&s=80" alt="{{ include.name }}">
+  </div>
+  <div class="comment__content-wrapper">
+    <h4 class="comment__author" itemprop="author" itemscope itemtype="https://schema.org/Person">
+      {% unless include.url == blank %}
+        <span itemprop="name"><a rel="external nofollow" itemprop="url" href="{{ include.url }}">{{ include.name }}</a></span>
+      {% else %}
+        <span itemprop="name">{{ include.name }}</span>
+      {% endunless %}
+    </h4>
+    <p class="comment__date">
+      {% if include.date %}
+        {% if include.index %}<a href="#comment{{ include.index }}" itemprop="url">{% endif %}
+        <time datetime="{{ include.date | date_to_xmlschema }}" itemprop="datePublished">{{ include.date | date: "%B %d, %Y at %I:%M %p" }}</time>
+        {% if include.index %}</a>{% endif %}
+      {% endif %}
+    </p>
+    <div itemprop="text">{{ include.message | markdownify }}</div>
+  </div>
+</article>