Added PyPy to the list of tested Pythons in .travis.yml.
Added pypy to tox.ini.
Added a note that mptt works on PyPy to the README.
Added the appropriate python version classifiers to setup.py.
Added Python 3.4 to the build process.
Added Python 3.5 to tox.ini.
Added Python 3.4 to the list of Python classifiers in setup.py.
Merge pull request #313 from thedrow/patch-1

PyPy and Python 3.4 support