Add html_link_suffix to correct linking issue

When you are searching for something and then
follow the link, it doesn't add the .html correctly
any more. This is to fix it.

source/conf-common.py

@@ -136,6 +136,9 @@ html_title = "Mahara {} manual".format(release)
 # A shorter title for the navigation bar.  Default is the same as html_title.
 html_short_title = "" # Left blank because a background image is placed in the css with text
 
+# Suffix for generated links to HTML files. The default is whatever html_file_suffix is set to; it can be set differently (e.g. to support different web server setups).
+html_link_suffix = '.html'
+
 # The name of an image file (relative to this directory) to place at the top
 # of the sidebar.
 #html_logo = None