Support custom parameters

[clphillips]

It would be great if custom parameters were supported. That is, equivalent to something like:

phpunit -c /path/to/phpunit.xml --do-something-special

This allows the bootstrap file access to the "do-something-special" parameter.

[ntwb]

This is a duplicate of #25, if I had the JavaScript skills I'd have a pull request to go with that ticket 😉

[clphillips]

I'm not so sure it's a dupe, given that 'd' is a specific command and was added recently to satisfy #25.