1. Sync sphinx dependency with global requirements. It caps python 2 since
sphinx 2.0 no longer supports Python 2.7.
2. Fix RST syntax in HACKING.rst
3. Update moved URLs in README.rst
Change-Id: I74bfead9b1962ad9c5e9eb2f7ab79022566085c9
According to preferred word choice document [1] we should use only
"OpenStack" term in our guides, READme documents and so on.
This patch fix our docs and other files according to these requirements.
[1] http://docs.openstack.org/contributor-guide/writing-style/word-choice.html
Change-Id: Iff395ad887f733245da338ec707b862a8ec42d8b