More CI

[KodrAus]

So there are a couple of ways to run cargo-nuget, which should all be tested on major platforms. I think there should be a couple of scenarios captured in containers and tested in CI, including:

• [ ] build a package with no arguments
• [ ] build a package with relative directories
• [ ] build a package with absolute directories

It would be good to have a scalable way to add more scenarios as the tool's complexity increases.