Add skeleton What's New and Upgrading docs for 5.2.

At present mostly consisting of XXX's.

doc/sphinx/whats-new/changes-5.2.rst

+.. _whatsnew_changes_5.2:
+
+Changes in Varnish 5.2
+======================
+
+*XXX: preamble*
+
+Varnish statistics
+~~~~~~~~~~~~~~~~~~
+
+*XXX: changes and new features of VSC/VSM*
+
+.. _whatsnew_new_vmods:
+
+New VMODs in the standard distribution
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+*XXX: introductory paragraphs about new VMODs*
+
+VMOD purge
+----------
+
+*XXX: about VMOD purge*
+
+VMOD vtc
+--------
+
+*XXX: about VMOD vtc*
+
+VMOD blob
+---------
+
+*XXX: about VMOD blob*
+
+XXX: Any other headline changes ...
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+*XXX: ...*
+
+News for authors of VMODs and Varnish API client applications
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+*XXX: such news may include:*
+
+* *XXX: effects of new VSC/VSM on VMODs*
+
+* *XXX: effects of new VSC/VSM on API client apps*
+
+* *XXX: changes in VRT*
+
+*EOF*

doc/sphinx/whats-new/index.rst

@@ -8,6 +8,15 @@ This section describes the changes and improvements between different
 versions of Varnish, and what upgrading between the different versions
 entail.
 
+Varnish 5.2
+-----------
+
+.. toctree::
+   :maxdepth: 2
+
+   changes-5.2
+   upgrading-5.2
+
 Varnish 5.1
 -----------
 

doc/sphinx/whats-new/upgrading-5.2.rst

+.. _whatsnew_upgrading_5.2:
+
+%%%%%%%%%%%%%%%%%%%%%%%%
+Upgrading to Varnish 5.2
+%%%%%%%%%%%%%%%%%%%%%%%%
+
+Varnish statistics and logging
+==============================
+
+*XXX: anything new for users or admins concerning statistics,*
+*varnishstat, logging etc*
+
+varnishd parameters
+===================
+
+* *XXX: -p params that are new, modified, deprecated or removed*
+
+* *XXX: use rst refs to keep it short*
+    
+* *XXX: ...*
+
+Changes to VCL
+==============
+
+*XXX: intro paragraph*
+
+*XXX: emphasize what most likely needs to be done, if anything,*
+*to migrate from 5.1 to 5.2*
+
+*XXX: ... or reassure that you probably don't have to do anything*
+*to migrate from 5.1 to 5.2*
+
+XXX: headline changes ...
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+*XXX: the most important changes or additions first*
+
+``req.hash`` and ``bereq.hash``
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+*XXX: about {be}req.hash, mention data type BLOB, advise about*
+*:ref:`vmod_blob(3)`*
+
+XXX: vcl_sub_XXX ...
+~~~~~~~~~~~~~~~~~~~~
+
+*XXX: list changes by VCL sub*
+
+XXX: more VCL changes ...
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+*XXX: any more details and new features that VCL authors have to know*
+
+vmod_std
+~~~~~~~~
+
+* *XXX: any changes in VMOD std?*
+
+New VMODs in the standard distribution
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+See :ref:`vmod_purge(3)`, :ref:`vmod_vtc(3)`, :ref:`vmod_blob(3)` and
+:ref:`whatsnew_new_vmods`.
+  
+Other changes
+=============
+
+* ``varnishstat(1)``:
+
+  * *XXX: changes due to new VSC/VSM*
+
+  * *XXX: ...*
+
+* ``varnishlog(1)``:
+
+  * *XXX: changes due to new VSC/VSM*
+
+  * *XXX: ...*
+
+* ``varnishtest(1)`` and ``vtc(7)``:
+
+  * *XXX: changes in test code*
+
+  * *XXX: for example due to VMOD vtc*
+
+  * *XXX: ...*
+
+* *XXX: any other changes in the standard VUT tools*
+
+  * *XXX: ...*
+
+* *XXX: changes in VRT that may affect VMOD authors*
+
+  * *XXX: ...*
+
+* *XXX: changes for developers?*
+
+  * *XXX: such as sanitizer flags?*
+
+  * *XXX: ...*
+
+* *XXX: other changes in tools and infrastructure in and around
+  Varnish ...*
+
+  * *XXX: anything new about project tools, VTEST & GCOV, etc?*
+
+  * *XXX: ...*