Support .NetStandard 1.5 or lower

[BennieCopeland]

Is there anything currently being used that prevents NSpec from targeting a lower .NetStandard? I have a test project per real project, but I have a Test.Runner project that references the other projects to run them all together. I've found it useful to have a single executable to run all the test projects, especially for code coverage generation. The problem is, the runner project is targeting .Net 4.6.2 (because not everything is .Net core yet), but I can't pull in those dotnet core test libraries, because .Net 4.6.2 can't include libs that target .NetStandard 1.6, only 1.5 or earlier. Since you are also targeting .Net 4.5.1, you could probably drop it down to .NetStandard 1.2.

[BrainCrumbz]

I do remember we tried to downgrade netstandard, when we first ported the framework from classic .NET to .NET Core. But I don't remember what blocked or prevented us from completing that. Would you give it a spin trying to build and see what happens?