Use travis-ci to run the tests

There is currently one test failure, unfortunately I don't know much about how this works. Would you be able to take a look @smizell?

```
FAIL: test_response_for (tests.wrappers_test.TestFlaskAPIResource)

AssertionError: Expected call: mock(<hypermedia_resource.base.HypermediaResource object at 0x7fa89ac95b90>, 'application/hal+json')
Not called
```