Adding initial stubs for PHPUnit unit tests

This commit also includes a few initial tests to get things started,
including tests for:

* Kite\CurlBack\Curl::__construct
* Kite\CurlBack\Curl::setAddress
* Kite\CurlBack\Curl::echoAddress
Merge pull request #11 from ramsey/phpunit-setup

Adds initial PHPUnit setup for the library