Target Framework - 472 Support

[Nyami]

Hello,

I was looking to integrate your package into a couple of projects to take advantage of the lob api, specifically address validation. However one of these projects is an older project and currently targets .NET Framework 4.7.2, and as this project targets netcoreapp3.1 we cannot take advantage of it.

Do you have plans, or have you considered, targeting other framework versions? I suspect you could target netstandard2.0 which would add support for a number of frameworks.

Cheers
Doug

[Nyami]

I've created a PR which I believe would address my issue, please feel free to disregard or modify if this doesn't align with your product goals etc.

Cheers
Doug