Update documentation for release

CRM/Stripe/AJAX.php

CRM/Stripe/Api.php

CRM/Stripe/Check.php

CRM/Stripe/Customer.php

CRM/Stripe/Form/UpdateWebhook.php

CRM/Stripe/Hook.php

CRM/Stripe/Upgrader.php

CRM/Stripe/Webhook.php

README.md

api/v3/Stripe/Cleanup.php

api/v3/Stripe/Ipn.php

api/v3/Stripe/Listevents.php

api/v3/Stripe/Populatelog.php

api/v3/Stripe/Setuptest.php

api/v3/StripeCustomer.php

api/v3/StripeSubscription.php

css/elements.css

docs/contribution.md

docs/hooks.md

docs/images/backend_cancelrecur.png