Simplify jinja2 base templates, update theme options

- New realfavicongenerator.net packages (https://realfavicongenerator.net/blog/new-favicon-package-less-is-more/)
- Support all possible Pelican feed links
- Add recommended HEAD elements (https://github.com/joshbuchea/HEAD)
- Use minified css assets
- Link to boostrap, clean-blog and font-awesome stylesheets
- Add theme options, better options names

Template consistency, update structure on base.html

Fix missing article summary on index.html

Show the article.summary for teasers

alchemy/templates/page.html

@@ -1,25 +1,24 @@
 {% extends "base.html" %}
 
 {% block head %}
-  {{ super() }}
-  {% if page.author %}
-    <meta name="author" content="{{ page.author }}">
-  {% endif %}
-  {% if page.summary %}
-    <meta name="description" content="{{ page.summary|striptags }}">
-  {% endif %}
-  <meta name="tags" contents="{% for tag in page.tags %}{{ tag }}, {% endfor %}">
+{{ super() }}
+{% if page.summary %}
+<meta name="description" content="{{ page.summary|striptags }}">
+{% endif %}
 {% endblock %}
 
 {% block title %}
-  {{ SITENAME }} &mdash; {{ page.title|striptags }}
+{{ page.title|striptags }} {{ super() }}
+{% endblock %}
+
+{% block page_header %}
+{{ page.title }}
 {% endblock %}
 
 {% block content %}
-  <div class="page">
-    <h1 class="title">{{ page.title }}</h1>
-    <div class="content">
-      {{ page.content }}
-    </div>
+<div class="page">
+  <div class="page-main">
+    {{ page.content }}
   </div>
+</div>
 {% endblock %}