Added a tox env for building Sphinx docs

Author: Nurdok

tox.ini

@@ -4,18 +4,24 @@
 # install tox" and then run "tox" from this directory.
 
 [tox]
-envlist = py26, py27, py32, py33, py34, py35, pypy, pypy3
+envlist = py26, py27, py32, py33, py34, py35, pypy, pypy3, docs
 
 [testenv]
 # Make sure reading the UTF-8 from test.py works regardless of the locale used.
 setenv = LANG=C LC_ALL=C
 commands = py.test --pep8 --clearcache
 deps = -rrequirements/tests.txt
 
+[testenv:docs]
+changedir=docs
+deps = -rrequirements/docs.txt
+commands=sphinx-build -b html . _build
+
 [pytest]
 pep8ignore =
     test.py E701 E704
 norecursedirs = docs .tox
 
 [pep257]
 inherit = false
+convention = pep257