SE-0500: Improving package creation with custom templates

[Honza_Dvorsky]

@jbute2000

I have added the changes to the implementation. Now, if version requirements are omitted, SwiftPM will try and find the latest SemVer compliant tag. If not, then it will throw an error.

Great, thank you. A big +1 for the proposal!

@Cyberbeni

Is this going to be used? I think people who wanted to create a template already have their template repository set up. At least I do.

Some projects surely did, but for example I'd love to adopt it in Swift OpenAPI Generator once available, but I never would have wanted to maintain bespoke template machinery myself.