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/simpleperf/trex.rst b/docs/usecases/simpleperf/trex.rst
index 996ed15..6d38ce5 100644
--- a/docs/usecases/simpleperf/trex.rst
+++ b/docs/usecases/simpleperf/trex.rst
@@ -65,7 +65,7 @@
            default_gw: 10.10.2.1
          - ip: 10.10.1.2
            default_gw: 10.10.1.1
-   
+
 Stop the previous VPP session and start it again in order to add a route for new
 IP addresses 16.0.0.0/8 and 48.0.0.0/8, according to Figure 2. Those IP addresses
 are needed because TRex generates packets that use these addresses. Refer to the
@@ -81,13 +81,13 @@
     __/ __/ _ \  (_)__    | | / / _ \/ _ \
     _/ _// // / / / _ \   | |/ / ___/ ___/
     /_/ /____(_)_/\___/   |___/_/  /_/
-   
+
    vpp# sho int
                  Name               Idx       State          Counter          Count
    FortyGigabitEthernet82/0/0        1        down
    FortyGigabitEthernet82/0/1        2        down
    local0                            0        down
-   
+
    vpp#
    vpp# set interface ip address FortyGigabitEthernet82/0/0 10.10.1.1/24
    vpp# set interface ip address FortyGigabitEthernet82/0/1 10.10.2.1/24
@@ -109,7 +109,7 @@
     Total-tx-bytes       : 166886 bytes
     Total-tx-sw-bytes    : 166716 bytes
     Total-rx-bytes       : 166886 byte
-   
+
     Total-tx-pkt         : 2528 pkts
     Total-rx-pkt         : 2528 pkts
     Total-sw-tx-pkt      : 2526 pkts