Add Travis CI and Coveralls

I've added a configuration file so Travis CI will build each commit and pull request. It runs against each Python version supported by Travis CI: 2.6, 2.7, 3.2, 3.3, 3.4, PyPy and PyPy3, and all of them pass with no changes needed. This will help maintain the codebase by automatically running the tests against all Python versions for each PR -- it's very handy for picking up those Py2/Py3 inconsistencies.. 

It also runs the tests with coverage enabled, and sends the coverage reports to Coveralls, so you can see how coverage changes, or if a PR doesn't include tests to cover its new code. Right now, inflect.py has an amazing 98% coverage!

You get reports like this:

 * https://travis-ci.org/hugovk/inflect.py
 * https://coveralls.io/r/hugovk/inflect.py

I've added badges to the README to show off how good stats this project has. Both Travis CI and Coveralls are free for open source project, you just need to enable them for the repo. Please can you do so at:

 * https://travis-ci.org/profile
 * https://coveralls.io/repos/new

Thanks!