Added support for the "retry" field.

[boenrobot]

Fixes #7

While the existing tests do pass, I'm not entirely sure how to make tests for this retry field yet... Just wanted to share the implementation. Some guidance to making tests for this will be appreciated.

[SimonFrings]

@boenrobot thanks for bringing this up 👍

As a starting point, I think you will find similar tests inside the EvenSourceTest.php file. It's nearly the same approach as the tests for 'id' and 'event'. We're always happy about 100% code coverage ;)

Does this help to get started?

[boenrobot]

Thanks.

I have added a test modeled after the last ID test.

[clue]

@boenrobot Thanks for looking into this, love the direction!

Also great to see this already has 100% code coverage in its current form. I've briefly checked the specs and noticed we should probably also check for valid values. In particular, a non-integer value should be ignored as per https://html.spec.whatwg.org/multipage/server-sent-events.html#event-stream-interpretation

Can you add some additional tests to cover this in MessageEventTest?

[boenrobot]

Good catch. That scenario was broken.

I've added a test with an invalid value (that initially failed; the retry timer was set to 0), added a check that would accept only ASCII digits as valid, and would cast the value to either int or float in case the message's value to int or float (if the retry value is beyond PHP_INT_MAX; Not very likely, I know, but still, the spec doesn't impose limits and React supports float timers, i.e. more than PHP_INT_MAX).

[clue]

@boenrobot Thank you for looking into this and your high-quality changeset, keep it up! 👍