remove carbon

Merge pull request #12 from eberkund/remove-composer-dep

Update composer.json

Merge pull request #9 from albertcito/api-version-2018-05-21

Added 2018-05-21 webhooks

Merge pull request #8 from alanms/api-version-2018-02-06

Added 2018-02-06 webhooks

Merge pull request #5 from jschutt/master

Added 2016-03-07 dummy webhooks

no support for 5.4

Delete InvalidEventException.php

update readme