Simplify requirements.

requirements.txt

-alabaster==0.7.7
-Babel==2.2.0
-docutils==0.12
-Jinja2==2.8
-MarkupSafe==0.23
 py==1.4.31
-Pygments==2.1
-pytest==2.8.7
-pytz==2015.7
-six==1.10.0
-snowballstemmer==1.2.1
-Sphinx==1.3.5
-sphinx-rtd-theme==0.1.9
+pytest==2.9.1
+-e .