Testing

I don't know if you plan to maintain / improve this library, however i have use for it so i allowed myself to fork this and improve the test suite to ensure filtering works.

I also added Travis and Coveralls and updated some requirements.

Anyway, i understand this is a big change and it may not be what you want to do with your lib (for instance, i made a switch to should and you may not approve). If this is the case, don't fear to say so and close the PR, and i'll continue to work on the other repo.
If however you're interested in improvements to the lib, i'll be delighted to help.

BTW, merging also fix #1.