Change data type from string to Uri

[vanillajonathan]

Changes the data type from string to Uri.

Instead of weakly typed string we use strongly-typed Uri that accurately conveys the underlying data and ensures proper data and semantics through validation of input.

Closes #386.

[vanillajonathan]

@leastprivilege I believe this CI might have failed because the Azure pipelines were down at that moment.
I think running it again would make the CI succeed.

[leastprivilege]

Thanks. That's a breaking change. We can consider this for the next major release.

[leastprivilege]

If you can resolve the conflicts today, I can put that into the v6 release

[vanillajonathan]

@leastprivilege Done!

[leastprivilege]

thanks!