[WIP] Linux build

[seif]

Couldn't build on linux otherwise. It still doesn't build, due to missing AssemblyVersion, but this moves us in the right direction.

[seif]

@Shatl a bunch of issues while trying to get this to run into linux, the main 2 so far are:
* multi targeting netstandard and net461 doesn't work on linux dotnet/sdk#826 do we need multi targeting? project built with net461 should be able to reference netstandard2.0.
* GitVersion crashes, not sure what is going on with it, I've disabled it and gone with default. Will figure out what is borken later.
* OpenCover doesn't support linux OpenCover/opencover#703 worth trying AltCover instead? This is what I'm stuck on at the moment.

[cd21h]

@seif Do you want to move whole build to Linux? We can have a hybrid build where code coverage and publish will run on Windows, while Linux build will just run unit-tests. In this case having hard-coded version on Linux builds should be enough. Do you have an idea how to do it with Appveyor ?

• 4.6.1. can be removed, I have no objections.

• GitVersion is needed for package publishing only.

[seif]

@Shatl cool, I've created various smaller PRs that include things I discovered here.

#187 fixes the file name casing
#188 Update github sourcelink
#189 remove net461

I'm hoping to get the same build running on CI and locally, so preferably we would have the coverage tool that runs on multi platforms. Initially, just getting to a stage where i can dotnet build dotnet test successfully would be good

[seif]

Closing this as the work has been done in other issues