Add internal init on struct to improve testing

[Thomaslegravier]

With swift 5 it's now impossible to add an extension of struct and implement a custom init.
It can be very useful for unit testing. In my case we use this method to create type components of a MockedStoreKit class.
I suggest to add internal init on type struct to permit init in unit testing context.

Swift evolution reference: https://github.com/apple/swift-evolution/blob/master/proposals/0189-restrict-cross-module-struct-initializers.md

[Sam-Spencer]

This looks like a great improvement. I'm all for adopting new language features for Unit Tests.

If you'd like, we're looking for contributors and maintainers for the repo -- check out the Slack channel.

Writing unit tests would be mightily appreciated too!

[Thomaslegravier]

Thanks @Sam-Spencer for feedback and approved my proposition.
Do you know when the next release will be?

[Sam-Spencer]

Yes! Check back this weekend for a new release! @Thomaslegravier