Adds initial PHPUnit setup for the library

This pull request provides initial setup for PHPUnit, along with a few working tests. All tests for the library should go in `Tests/Kite/CurlBack`. There is already a `CurlTest` class in place, with stub methods generated by [PHPUnit Skeleton Generator](http://www.phpunit.de/manual/current/en/skeleton-generator.html). I have provided tests that cover the following methods:

* __construct
* addAddress
* echoAddress

You should be able to simply run `phpunit` from the root of the project (where the phpunit.xml.dist file is located), and it will run the tests for you, provided you have [PHPUnit installed](http://phpunit.de/).

Let me know if you have any questions, and I'll be happy to provide direction, but I hope this gives you a good start on writing unit tests for the library.