Add boilerplate for Sphinx doc rendering

This is the necessary boilerplate configuration to be able to run
Sphinx via PBR from tox and render reStructuredText into HTML for
publication. Also add the httpdomain contrib plugin for Sphinx since
this project will include some HTTP API documentation.

Change-Id: Ied0092e2965463abe0c86d37047faa6b47d1bc97

tox.ini

@@ -0,0 +1,22 @@
+[tox]
+minversion = 1.6
+envlist = docs
+
+[testenv]
+install_command = pip install -U {opts} {packages}
+setenv =
+   VIRTUAL_ENV={envdir}
+deps = -r{toxinidir}/requirements.txt
+
+[testenv:venv]
+commands = {posargs}
+
+[testenv:docs]
+commands = python setup.py build_sphinx
+
+[testenv:spelling]
+deps =
+   -r{toxinidir}/requirements.txt
+   sphinxcontrib-spelling
+   PyEnchant
+commands = sphinx-build -b spelling doc/source doc/build/spelling