Add -A option to pass values into HTML templates.

tests/root/_templates/layout.html

@@ -0,0 +1,4 @@
+{% extends "!layout.html" %}
+{% block extrahead %}
+<meta name="hc" content="{{ hckey }}" />
+{% endblock %}

tests/root/conf.py

@@ -133,6 +133,8 @@ html_last_updated_fmt = '%b %d, %Y'
 # If nonempty, this is the file name suffix for HTML files (e.g. ".xhtml").
 #html_file_suffix = ''
 
+html_context = {'hckey': 'hcval'}
+
 # Output file base name for HTML help builder.
 htmlhelp_basename = 'SphinxTestsdoc'