Dialogflow PHP webhook handler

Dialogflow PHP webhook handler by Chua Chee Wee.

Use with https://dialogflow.cloud.google.com/

• Under Fulfillment page, set Fulfillment URL to point to process.php.
• Under Intents page, set Action to GetMultiply, GetSum, ie, the various handlers in PHP and set parameter to number and number2.Also, check "Enable webhook call for this intent" under Intents page.

Auth keys have been removed.