New LTP documentation

[Petr Vorel]

Hi all,

today I merged Andrea's and Cyril's work migrating our GitHub based docs to
readthedocs.org. Andrea, Cyril, thank you for this work, we're now using for
docs the same approach as the Linux kernel.

Our new documentation is now on https://linux-test-project.readthedocs.io/en/latest/.

I configured the hook on readthedocs.org, thus any docs update should trigger
readthedocs.org rebuild.

I also disabled our wiki on GitHub [2], it redirects to our homepage. It would
be good to be able to redirect it to our new readthedocs.org docs [1].

I also remove (with Cyril's ack) the content of our github.io page [3] to our
new readthedocs.org docs [1].

The docs is mostly done, but some bits are missing (e.g. C Test Network API [4],
KVM Test API [5], shell API [6]), thus we kept them in doc/old folder. This
folder will be removed once we finish the migration.

Kind regards,
Petr

[1] https://linux-test-project.readthedocs.io/en/latest/
[2] https://github.com/linux-test-project/ltp/wiki/
[3] https://linux-test-project.github.io/
[4] https://github.com/linux-test-project/ltp/blob/master/doc/old/C-Test-Network-API.asciidoc
[5] https://github.com/linux-test-project/ltp/blob/master/doc/old/KVM-Test-API.asciidoc
[6] https://github.com/linux-test-project/ltp/blob/master/doc/old/Shell-Test-API.asciidoc