docs: Relative links improvements

- replace two separate blocks for previous and next chapter on side
  bar with common 'Navigation' block;
- add link to table of contents to the block, as it's not that easy
  to find one in current layout.

Change-Id: Iabb191fa94ac9bcb061db8e90d69c87525965527

doc/source/conf.py

@@ -20,7 +20,7 @@ extensions = [
 # execute "export SPHINX_DEBUG=1" in your terminal to disable
 
 # Add any paths that contain templates here, relative to this directory.
-# templates_path = []
+templates_path = ['templates']
 
 # The suffix of source filenames.
 source_suffix = '.rst'

doc/source/templates/layout.html

@@ -0,0 +1,15 @@
+{% extends "!layout.html" %}
+{% block sidebarrel %}
+  <h3>{{ _('Navigation')}}</h3>
+  <ul>
+{% if pagename != "index" %}
+    <li><a href="{{ pathto(master_doc) }}">{{ _('Table Of Contents') }}</a></li>
+{% endif %}
+{% if next %}
+    <li><a href="{{ next.link|e }}" title="{{ _('next chapter') }}">{{ _('Next topic') }}: {{ next.title }}</a></li>
+{% endif %}
+{% if prev %}
+    <li><a href="{{ prev.link|e }}" title="{{ _('previous chapter') }}">{{ _('Previous topic') }}: {{ prev.title }}</a></li>
+{% endif %}
+  </ul>
+{% endblock %}