add batch events method

[ice6]

trafficstars

ccording to the https://docs.prediction.io/datacollection/eventmodel/#3-batch-events-to-the-eventserver code tested, the code works in my 0.9.5 environment

[pferrel]

@EmergentOrder @mkorolyov We need to do this for the java SDK too

[pferrel]

@ice6 do you know why the build failed for PHP 9.5 failed?

[ice6]

@pferrel see https://travis-ci.org/PredictionIO/PredictionIO-PHP-SDK/jobs/97362609 the log shows that the ci env is broken :) not because of the code (btw. PHP5.5 not PHP9.5)

@dantudor thanks, code refactored :)