docs: better docs, mv doxygen to sphinx

This patch refactors the VPP sphinx docs
in order to make it easier to consume
for external readers as well as VPP developers.

It also makes sphinx the single source
of documentation, which simplifies maintenance
and operation.

Most important updates are:

- reformat the existing documentation as rst
- split RELEASE.md and move it into separate rst files
- remove section 'events'
- remove section 'archive'
- remove section 'related projects'
- remove section 'feature by release'
- remove section 'Various links'
- make (Configuration reference, CLI docs,
  developer docs) top level items in the list
- move 'Use Cases' as part of 'About VPP'
- move 'Troubleshooting' as part of 'Getting Started'
- move test framework docs into 'Developer Documentation'
- add a 'Contributing' section for gerrit,
  docs and other contributer related infos
- deprecate doxygen and test-docs targets
- redirect the "make doxygen" target to "make docs"

Type: refactor

Change-Id: I552a5645d5b7964d547f99b1336e2ac24e7c209f
Signed-off-by: Nathan Skrzypczak <nathan.skrzypczak@gmail.com>
Signed-off-by: Andrew Yourtchenko <ayourtch@gmail.com>
diff --git a/docs/usecases/vhost/vhost03.rst b/docs/usecases/vhost/vhost03.rst
index ed58334..05d1fd1 100644
--- a/docs/usecases/vhost/vhost03.rst
+++ b/docs/usecases/vhost/vhost03.rst
@@ -17,7 +17,7 @@
     vpp# show bridge 100 det
       BD-ID   Index   BSN  Age(min)  Learning  U-Forwrd  UU-Flood  Flooding  ARP-Term  BVI-Intf
        100      1      0     off        on        on        on        on       off       N/A
-    
+
                Interface           If-idx ISN  SHG  BVI  TxFlood        VLAN-Tag-Rewrite
          VirtualEthernet0/0/0        3     1    0    -      *                 none
        TenGigabitEthernet86/0/0      1     1    0    -      *                 none
@@ -85,4 +85,4 @@
                                                          tx packets                    16
                                                          tx bytes                    1476
     local0                            0        down
-    vpp# 
+    vpp#