vonage-php-sdk-core Beta 4 - More Call API Support

:hammer: Changed how underlying collection / resource concepts are applied:

Moving to both collections and resources being client aware.

Moving away from the concept of each API having a ‘client’ (now represented by collections / resources)

:sparkles: Added live call support:

$call->stream->setUrl($url);
$call->stream->put();
Need to add fluent interface, and some convience methods.

:sparkles: Can pass arbitrary data to JWT generation:

Per general spec (#22)

:hammer: Update of signature generation:

Based on changes to the API: #29