Update Sender#send to be only method for sending
Update Sender#send to be only method for sending

* The following methods were removed:
  * Sender#sendNoRetry
  * Sender#sendMulti
  * Sender#sendNoRetryMulti
* Sender#send now accepts a single or array of registration ids to send to.
* The number of retries is now configurable via Sender#retries.
* Improved error handling in Sender

lkorth/php-gcm,lkorth/php-gcm