Adds Unit Tests

Adds a composer.json to include phpunit as a developer dependency. Adds
a .gitignore file to ignore vendor and bin directory resulting from a
composer install.

Adds a phpunit.xml.dist file with basic test suites setup. Adds a test
bootstrap file to bring in the required classes for our tests.

Adds unit tests for all currently public methods in Gitphull.php to
ensure functionality is working correctly.

Fixes a bug where new branches cloned from Gitphull are not cloned into
the proper branch.

Edits setLocation to add a trailing slash if one is not included.