Initialize readthedocs documentation for integration/packaging

Initialize readthedocs documentation for integration/packaging

You can build the docs with:

    tox -edocs

and view the docs by opening:

    firefox .tox/docs/tmp/html/index.html

This patch simply initializes sphinx for integration/packaging. Once
merged we can link into the docs project and have it generated on
readthedocs under the docs project's readthedocs link:

    https://opendaylight.readthedocs.io/en/latest/

Change-Id: I9ba9a5048f043a8fee9bacf66db867c27f616bce
Signed-off-by: Thanh Ha <thanh.ha@linuxfoundation.org>