Add doc building to CI

Author: hynek

.travis.yml

@@ -7,6 +7,7 @@ env:
     - TOX_ENV=pypy
     - TOX_ENV=flake8
     - TOX_ENV=manifest
+    - TOX_ENV=docs
 
 install:
     - pip install tox coveralls

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = py27, py33, py34, pypy, flake8, manifest
+envlist = py27, py33, py34, pypy, flake8, manifest, docs
 
 [testenv]
 deps =
@@ -19,3 +19,10 @@ deps =
     check-manifest
 commands =
     check-manifest
+
+[testenv:docs]
+basepython = python2.7
+deps =
+    sphinx
+commands =
+    sphinx-build -W -b html -d {envtmpdir}/doctrees docs docs/_build/html