Drop .NET 2.0, netstandard1.1 support

[qmfrederik]

Works toward #435

[qmfrederik]

Looks like there's a build failure on uap10.0. I don't know much about UAP.
I kept net45 for now as I have a customer which is still on that platform 😄 .

[AArnott]

It looks more to me like cabinet.csproj is causing the problem in the build. Is it targeting netstandard1.3?

D:\a\1\s\src\Cabinet\Cabinet.csproj : error NU1201: Project CodeGenerationAttributes is not compatible with netstandard1.3 (.NETStandard,Version=v1.3). Project CodeGenerationAttributes supports: [D:\a\1\s\src\PInvoke.sln]
D:\a\1\s\src\Cabinet\Cabinet.csproj : error NU1201:   - net45 (.NETFramework,Version=v4.5) [D:\a\1\s\src\PInvoke.sln]
D:\a\1\s\src\Cabinet\Cabinet.csproj : error NU1201:   - netstandard2.0 (.NETStandard,Version=v2.0) [D:\a\1\s\src\PInvoke.sln]
D:\a\1\s\src\Cabinet\Cabinet.csproj : error NU1201:   - uap10.0 (UAP,Version=v10.0) [D:\a\1\s\src\PInvoke.sln]