Merge "Add a tox environment to build the docs"

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = heka,lma_collector
+envlist = heka,lma_collector,docs
 skipsdist = True
 
 [testenv:heka]
@@ -27,3 +27,10 @@ commands =
     mkdir -p {toxinidir}/.bundled_gems
     bundle install
     bundle exec rake test
+
+[testenv:docs]
+deps = -r{toxinidir}/test-requirements.txt
+changedir = {toxinidir}/doc
+whitelist_externals = make
+commands =
+    make clean html SPHINXOPTS=-W