feat: major improvements

[bdovaz]

I've done a lot of things, you can really see it in the README.md file in the Advanced usage section.

If you're still interested in maintaining this project (I hope you are), I'll add you as the owner of the NuGet package.

Highlights:

• Stop hardcoding as much as possible and make it parameterizable so that it is compatible even with Unity packages and not just with the editor.
• Project converted to cli distributed in NuGet as a cross platform dotnet tool.
• There is a main command that generates the xrefmap file.
• There is a test command that, when passed an xrefmap file, allows you to test the links in the href field.
• Test the cli commands.
• Patch a few more cases with string replace so that it generates the documentation correctly.

I haven't fixed the github pages workflow in this PR (it's been failing since November 2024) with the new changes because, at the very least, this PR dotnet/docfx#10827 that I created due to a problem that occurs when trying to generate the UnityEngine xrefmap needs to be merged.

[bdovaz]

@NormandErwan ping!