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/gettingstarted/progressivevpp/routing.rst b/docs/gettingstarted/progressivevpp/routing.rst
index c9586c1..38841b7 100644
--- a/docs/gettingstarted/progressivevpp/routing.rst
+++ b/docs/gettingstarted/progressivevpp/routing.rst
@@ -50,10 +50,10 @@
 
    $ sudo ip route add 10.10.2.0/24 via 10.10.1.2
    $ ip route
-   default via 10.0.2.2 dev enp0s3 
-   10.0.2.0/24 dev enp0s3  proto kernel  scope link  src 10.0.2.15 
-   10.10.1.0/24 dev vpp1host  proto kernel  scope link  src 10.10.1.1 
-   10.10.2.0/24 via 10.10.1.2 dev vpp1host 
+   default via 10.0.2.2 dev enp0s3
+   10.0.2.0/24 dev enp0s3  proto kernel  scope link  src 10.0.2.15
+   10.10.1.0/24 dev vpp1host  proto kernel  scope link  src 10.10.1.1
+   10.10.2.0/24 via 10.10.1.2 dev vpp1host
 
 Setup return route on vpp2
 ---------------------------