[WIP] Csproj2017 + .NET standard 2

[304NotModified]

fixes #34 , fixes #41

todo

• [x] package setup in csproj
• [x] .net45/46 unit tests wont run on appveyor

Starting test execution, please wait... No test is available in C:\projects\fody-stamp\Tests\bin\Release\net452\Tests.dll. Make sure that test discoverer & executors are registered and platform & framework version settings are appropriate and try again.

• [ ] fix nupkg