Improve the Kumite API to make logging same events for multiple experiments easier

[creativej]

Currently we can only log one event at a time using:

Kumite::event($testKey1, $eventName, $data);
Kumite::event($testKey2, $eventName, $data);

If it can accepts an array of test keys then it would be much nicer

Kumite::event(array($testKey1, $testKey2), $eventName, $data);