Add docs target build for tox

tox.ini

@@ -4,7 +4,7 @@
 # and then run "tox" from this directory.
 
 [tox]
-envlist = py34, py27
+envlist = py34, py27, docs
 
 [testenv]
 commands = {envpython} setup.py test
@@ -13,4 +13,13 @@ deps = pexpect
        pycrypto
        colorama
        pymysql
+       psycopg2
+       pymongo==2.8
 sitepackages=True
+
+[testenv:docs]
+changedir = docs
+deps =
+  sphinx
+commands =
+  sphinx-build -b html -d {envtmpdir}/doctrees source {envtmpdir}/html