Realtime optional

Enables an option in the guardfile to specify realtime output

Adding `:realtime => true` to the options list in a project's `Guardfile` will enable use of a new `RealtimeRunner` that uses `phpunit`'s `--log-json` option to parse a log.

This removes the necessity to parse `phpunit`'s output.

For large PHPUnit test suites, this allows the dots to be printed in real time