Add automated testing with Travis
Install numpy before performing the builds
Use the right numpy system package depending on the Python version
Installing the python3-numpy system package alone did not do the trick on Python 3 for some reason (why this works on Python 2 I'm not even sure).  This *might* do the trick though, by symlinking the system package into the virtualenv's site-packages.
Include a symlink to the egg-info directory too to allow pkg_resources to recognize that numpy is installed
Apparently the system python3-numpy still won't work on Python 3.3 probably due to a binary incompatibility. I think this can be resolved by just installing Numpy with pip via a wheel as we do on Astropy, but in the meantime I'm just leaving 3.3 disabled.
Merge pull request #30 from embray/travis

Add automated testing with Travis