documentation/source/conf.py: Optionally use the read the docs theme

If available, use the read the docs theme to build
the documentation.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
documentation/source/conf.py: Update version and copyright info

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>