[Do Not Merge] NetStandard Upgrade: Update NuSpec & Raw NuGets

[jamesmontemagno]

Should now install in just about every application

[jamesmontemagno]

@onovotny can you validate my changes here.

[clairernovotny]

Overall, the changes look ok to me

[clairernovotny]

NETStandard.Library 1.6.1 is better since it has fixes for Xamarin related issues with certain PCL profiles

[jamesmontemagno]

sounds good :) yeah I see that is the default now of file new

[clairernovotny]

Also, do you want dependency groups for Xamarin tvOS and watchOS?

[jamesmontemagno]

I think this library itself is still actually a PCL which is really odd, I am going to change it over to .NET Standard 1.1 and then add tvos/watchos

[jamesmontemagno]

Alright @onovotny I think this should be good now, I have created a new .NET Standard 1.1 project and added in the references needed.

I am not sure how this will build on a mac though... I assume it will be alright.... @praeclarum may want to switch over to appveyor for the VS 2017 build

[jamesmontemagno]

I think that once Bitrise upgrades to the latest stable it will build up.

[clairernovotny]

@jamesmontemagno if you're going that approach, you can just use the pack targets too -- dotnet pack. All of the info in the nuspec have equivalent properties in the csproj. The only reason to really split out the dependency groups as you have them would be to potentially minimize pain on people using packages.config with older project types.

[praeclarum]

I have been working on a new version of this that builds using .NET Core on Bitrise.

I'm making good progress! Let's switch to there.

#561