Add Assertions for "Plus Sign Alias" Email Addresses

[shawnhooper]

This pull request adds two assertions to support email addresses like:

myname+spam@example.com

This type of "plus sign alias" is supported by GMail, Office365, and several other providers. I couldn't find an official name for this feature, and am open to alternate naming suggestions.

New Assertions

EmailAssertions::assertPlusMailbox('myname, 'myname+spam@example.com')
EmailAssertions::assertPlusAlias('spam', 'myname+spam@example.com');

[Gummibeer]

Thanks a lot for this contribution! 🙏
Pretty cool extension to that package. 🎉
Sorry for the delay, with a new job I didn't had much time for OSS during the last weeks. 😟

[Gummibeer]

https://github.com/Astrotomic/phpunit-assertions/releases/tag/0.5.0

[shawnhooper]

@Gummibeer Thanks for the merge Tom! Cheers.