Recipients are broken since 1.19.1

[pascaldevink]

I believe 1.19.1, which featured #103 should not be released as a minor change, but rather in a new major version release, as it's not backwards compatible:

1. Since the types changed, all code using recipients as arrays broke.
   Previously, this worked fine:

$messageBirdMessage->recipients = [$number];

But that now breaks.
2. The Recipient class defines the $recipient property as integer (https://github.com/messagebird/php-rest-api/blob/master/src/MessageBird/Objects/Recipient.php#L16), while that formerly accepted a string, which can still be seen in the examples (https://github.com/messagebird/php-rest-api/blob/master/examples/message-create.php#L9). The original documentation also shows that string values are allowed (https://developers.messagebird.com/quickstarts/sms/send-sms-curl/), so why this changed is unclear. This doesn't break code as much, as it's not strictly enforced by the compiler, but does break PHPStan checking my code.
3. Examples have not been updated, so documentation is now very confusing for new users.

All-in-all, I think the best course of action now would be to:

1. Revert the changes in 1.19.1, releasing 1.19.2 as a fix
2. Fix the documentation, examples and types
3. Release 2.0 with this change again

[modprobe]

Hi @pascaldevink! You are right, that was my oversight 🤦 I have reverted the PR and released v1.19.2 with the fix.

@JohnstonCode fyi. I think your code was good, but we both missed the assignment side of this. Please feel free to submit an improved version of your PR with no changes to BC again 🙏

[pascaldevink]

@modprobe Thanks! The change is certainly good, no argument there 🙂