Add Travis config

Travis will need to be switched on for this repo via:
https://travis-ci.org/profile

Note: Due to #10 the tests currently fail for pip 8.1.2.

.travis.yml

@@ -0,0 +1,12 @@
+sudo: false
+language: python
+python:
+  - "2.7"
+  - "3.4"
+  - "3.5"
+  - "pypy"
+cache: pip
+install:
+  - pip install -r requirements.txt
+script:
+  - tox

README.rst

@@ -1,6 +1,9 @@
 pip-pop
 =======
 
+.. image:: https://travis-ci.org/kennethreitz/pip-pop.svg?branch=master
+    :target: https://travis-ci.org/kennethreitz/pip-pop
+
 Working with lots of ``requirements.txt`` files can be a bit annoying.
 Have no fear, **pip-pop** is here!