Added opportunity to click on calendar to view it in a larger format

Fixes #1025

Author: art-dr

doc/release/releases_calendar.svg renamed to doc/release/_images/releases_calendar.svg

@@ -481,7 +481,8 @@ Currently supported versions visualised as a calendar:
 
 .. ifconfig:: builder not in ('latex', )
 
-    .. image:: releases_calendar.svg
+    .. image:: _images/releases_calendar.svg
+        :target: _images/releases_calendar.svg
         :align: left
         :alt: releases_calendar.svg