Add support for specifying path to phpunit to avoid reliance on global install

[gunnarlium]

Now that phpunit has added support for installation via composer, it's easier to have local install per project, and thus avoid conflicts generated by global installs of phpunit.

If you could add an optional parameter for specyfing path to phpunit, I believe this would work great.

[MPV]

Can this be closed as a duplicate of #7?

[gunnarlium]

Yes.