Split up the hitrate chapter into four and added a introduction to ESI. ESI...

Split up the hitrate chapter into four and added a introduction to ESI. ESI needs a bit of work wrt params and operational factors.

git-svn-id: http://www.varnish-cache.org/svn/trunk/varnish-cache@5576 d4fa192b-c00b-0410-8231-f00ffab90ce4

doc/sphinx/tutorial/index.rst

@@ -22,6 +22,10 @@ separate topic. Good luck.
 	vcl
         statistics
         increasing_your_hitrate
+	cookies
+	vary
+	purging
+	esi
 	advanced_backend_servers
         handling_misbehaving_servers
         advanced_topics