MS Config and DependencyModel refs updated

[MV10]

Per #83, updated and tested references to Microsoft.Extensions.DependencyModel
and Microsoft.Extensions.Configuration.*. Updated .NET Standard from 1.6 to 2.0.

Confirmed both framework sample versions also run correctly. In all project files, old .NET Framework and .NET Standard refs were updated separately (conditional TFMs) to latest supporting versions. Also added a comment to the test project explaining how to run the multi-targeted tests from the command line (it was new to me, I suspect it is not commonly known).

[MV10]

I've never used Travis, not sure why it blows up with a netstandard1.6 error... there is nothing left in any part of the project which references it. Everything else works, hopefully it's an easy fix.

Also, didn't bump the version, not sure whether you'd consider this a minor or patch change.

/usr/share/dotnet/sdk/2.1.4/Sdks/Microsoft.NET.Sdk/build/Microsoft.PackageDependencyResolution.targets(167,5): error : Assets file '/home/travis/build/serilog/serilog-settings-configuration/src/Serilog.Settings.Configuration/obj/project.assets.json' doesn't have a target for '.NETStandard,Version=v1.6'. Ensure that restore has run and that you have included 'netstandard1.6' in the TargetFrameworks for your project. [/home/travis/build/serilog/serilog-settings-configuration/src/Serilog.Settings.Configuration/Serilog.Settings.Configuration.csproj]

[adamchester]

Hey @MV10, you should try changing buld.sh which is locked to netstandard1.6

[MV10]

@adamchester Thanks! The file isn't in the SLN view and I didn't think to jump back to the file view. All good now, much appreciated.

[nblumhardt]

LGTM! Just wondering if we need to define APPDOMAIN for the netstandard2.0 target for completeness, now? Or if we can remove it entirely? (Not sure why we use it in this lib.)

[nblumhardt]

Are the features behind #if APPDOMAIN now usable on .NET Standard 2.0?

[MV10]

Since APPDOMAIN was specific to net451 I didn't give it any consideration. The only use is here. Frankly, I'm not really clear about what that bit of code is meant to accomplish, but all that System.IO path and directory stuff is Windows-specific, so I assume .NET Standard / Core doesn't need this, and I would expect the existing code can remain unchanged.

To be honest, my focus in this change was updating MS Config to v2, so as long as the DependencyModel stuff built and tested clean, I figured it was good. But I'm happy to expand on the PR if you think something else is needed.

[nblumhardt]

Ah, great 👍 - that code enables using types without listing all of the assemblies in serilog:using keys on the full framework. It probably will kick in when targeting .NET Framework using the .NET Standard 2.0 targets, so perhaps we remove the #if and enable it on all platforms? I'm reasonably certain AppDomain.BaseDirectory is available on .NET Standard 2.

[MV10]

@nblumhardt Good call, you're right. I'd moved netstandard2_0 to be the first TFM which makes VS default to that, so as a first look Intellisense was satisfied without the constant. Builds ok, tests pass, Travis is happy.

Not sure why I thought System.IO was framework-level rather than standard-API. I suppose I haven't had much call for raw file I/O lately. Anyway, I think we're good to go: newer libs and less code, can't argue with that!

[nblumhardt]

👍

We might have to see how the combined Framework 4.5.1/Standard 2.0 targeting works out in practice - have had some issues with this kind of setup in the past; shouldn't be any trouble dropping 4.5.1 support from 3.0.0 of this package if we end up having to.

Thanks for your efforts, @MV10 !