Theme-related Documentation Enhancements

- Consistent background color in all types of codes
- Improve dd (list item) padding
- Link to Index in global TOC in navbar
- Briefly describe Instaloader in `index.html` title
- Remove page contents (navbartoc) in index, genindex and installation
- Link to new pypi.org rather than old pypi.python.org

docs/_templates/layout.html

@@ -1,4 +1,11 @@
 {% extends "!layout.html" %}
+{% block htmltitle %}
+  {% if pagename == "index" %}
+  <title>{{ title|striptags|e }}</title>
+  {% else %}
+  <title>{{ title|striptags|e }}{{ titlesuffix }}</title>
+  {% endif %}
+{% endblock %}
 {% block extrahead %}
 {{ super() }}
   <meta name="google-site-verification" content="FNUsDdkOJM9obm9QEdrNBVd9AtAzHzA-aaSMCUrS6C8" />