* Rename SebastianBergmann\Git to SebastianBergmann\Git\Git
* Eliminate pass-by-reference arguments in private
* SebastianBergmann\Git\Git::execute() method
* Introduce SebastianBergmann\Git\Exeption and SebastianBergmann\Git\RuntimeExeption
* Throw an SebastianBergmann\Git\RuntimeExeption when the command executed by SebastianBergmann\Git\Git::execute() exits with a status code other than 0
* Bump version number to 2.0-dev