Merge nuspec and CommonAssemblyInfo into csproj

[scott-xu]

Suggest using Nerdbank.GitVersioning after this PR

[Rob-Hague]

Will you also delete https://github.com/sshnet/SSH.NET/blob/develop/build/nuget/SSH.NET.nuspec?

(assuming this works well with sandcastle etc.)

[scott-xu]

Will you also delete https://github.com/sshnet/SSH.NET/blob/develop/build/nuget/SSH.NET.nuspec?

(assuming this works well with sandcastle etc.)

I didn't delete the nuspec because I need confirmation from @WojciechNagorski.

[scott-xu]

Regarding sandcastle, it would be good to migrate to docfx

[scott-xu]

Will you also delete https://github.com/sshnet/SSH.NET/blob/develop/build/nuget/SSH.NET.nuspec?
(assuming this works well with sandcastle etc.)

I didn't delete the nuspec because I need confirmation from @WojciechNagorski.

@WojciechNagorski@drieseng , what do you think? Should we delete SSH.NET.nuspec?

[WojciechNagorski]

@scott-xu I'm sorry that the review is delayed, but I need more time to think and review it thoroughly.

[Rob-Hague]

It looks good. Before (using build/build.proj per the wiki):

Details

After (using dotnet pack):

Details

I think the next steps are:

1. Delete the nuspec
2. Modify build.proj to use dotnet pack instead of nuget.exe

Would it be possible to do these in this PR? That way we don't end up with two different ways to generate the release artifacts, and the new nuget method should integrate seamlessly into the current release process (which will also help with validation).

After that (in another PR) maybe we can call build.proj in CI to generate the artifacts.

[WojciechNagorski]

I will try to find time next week for this PR