Adds a rudimentary testing framework

Hey there @picklepete!  I wonder if I could borrow a few minutes of your time to check out this PR that will add a basic testing framework that users can add tests to in the future.

This PR adds the following:
* **Tox/py.test Testing Support**: Run `tox` to run tests on all supported versions of Python (currently only Python 2.6 and Python 2.7), or just run `py.test` to run the tests on your environment's Python version.
* **Travis-ci Integration**: Adds a reasonable `.travis.yml` that will test both merged contributions and pull requests by running:
  * `pep8` to check for [PEP-8 style guide](http://legacy.python.org/dev/peps/pep-0008/) compliance.
  * `py.test` in all supported versions of Python to ensure that nothing new has broken.

It will take just a minute more of your time to enable Travis-ci integration, though -- it can be enabled only by the repository owner.

1. Go to https://travis-ci.org/ and log-in.  It will use your Github credentials.
2. Go to [your profile](https://travis-ci.org/profile/picklepete) and flip the switch for `picklepete/pyicloud`.

Cheers, and thanks for having a glance!