Added dev requirements file. Updated travis config

Author: Dan

.travis.yml

@@ -13,8 +13,7 @@ matrix:
 before_install:
   - pip install -U pip setuptools
 install:
-  - pip install -r requirements.txt
-  - pip install coveralls flake8 sphinx
+  - pip install -r requirements-dev.txt
 script:
   - nosetests --with-coverage --cover-package=pssh
   - flake8 pssh

requirements-dev.txt

@@ -0,0 +1,6 @@
+coveralls
+flake8
+sphinx
+sphinx_rtd_theme
+nose
+-e .