Do automatic release to PyPi from Travis CI

As commented by @glyph  in #83 it would be nice to have automatic deployment to PyPi.

Travis CI has support for this http://docs.travis-ci.com/user/deployment/pypi/

I have pushed an initial change to travis config file.

I think that is better to create a new PyPi account dedicated for this auto publishing process.

To have this working someone need to create an account on PyPi and send me the encrypted password.

Another option, is to give me permissions to PyPi and GitHub for twistedcheker project, and I can take care of the rest.

Thanks!