fix(spdx): adds support for reading ReferenceCategories with hyphens

[andreas-hilti]

Fixes #267

builds upon #268

also fixes an issue with deserialization of localized DateTime

[mtsfoni]

This topic is a little much.
I understand with this PR we can read underscore as well as hyphen and output underscore? Is that correct?

Stupid Question: Would outputting it with a hyphen make more sense, since that seems to be the general naming convention at SPDX for those things?

[andreas-hilti]

This topic is a little much.

I hope we are done with it afterwards for a while...

I understand with this PR we can read underscore as well as hyphen and output underscore? Is that correct?

Yes, this is the idea.

Stupid Question: Would outputting it with a hyphen make more sense, since that seems to be the general naming convention at SPDX for those things?

There are no stupid questions, I focused mainly to get main merged into it. Xml was already using hyphen; I have now adapted Json as well.