Add .travis.yml

Enable support Travis CI tests to be run at every commit pushed to
the GitHub repository
Add limited support for Scipy 0.9.0

Change scipy imports so that Icarus can be used almost entirely
without needing Scipy 0.12.0+. Now all Icarus functionalities
can be used with Scipy 0.9.0 with the exception of zipf_fit
function, which requires Scipy 0.12+