Merge pull request #11 from nickveenhof/master

Lowering requirements for the git wrapper - hopefully it still works OOTB
Converted docs to Doxygen format, added a doxygen.conf file.
Changed name of doxygen.conf to the default Doxyfile.
Finalized documentation.
Fixed #12: Added checks to the setPrivateKey() to ensure that the passed paths can be resolved.
Removed superfluous method calls, refactored to promote code reuse across the GitWrapper::git() and GitWrapper::run() methods, added methods to set parameters passed to the Process::run() method.
Fixed comments, renamed variables for consistency, implemented EventDispatcherInterface.
Added git.command.success and git.command.error events, added __toString() magic method for the working copy.
Added support for the git tag command.
Fixed misnamed error event in GitEvents.
Added skeleton test classes and Travis CI files.
Fixed #14: Added use commands for missing classes.
Added skeleton classes.
Renamed phpunit.xml file.
Added composer install prior to running tests.
Added Travis CI build status image to readme file.
Added tests for all set / get methods in the wrapper.
Added command failure tests, separated some base methods into a GitWrapperTestCase class.
Added wrapper error tests, added test to ennsure the wrapper script is executable.
Completed test coverage of the GitWrapper class, added tests for GitWorkingCopy.