Travis CI

To ensure the tests are run and pass when pushing to the repo and help prevent issues like [this](https://github.com/project-imas/encrypted-core-data/pull/106#commitcomment-7448547) I've added a `.travis.yml` file and a status badge to the `README.md`.

You'll have to go to the [Travis accounts](https://travis-ci.org/profile) page to enable the repo to work with Travis!

Though the build is currently failing due to the above commit.

Cheers for the library and work again :)