Target .NET Standard 1.3

[AArnott]

Adds .NET Core support (by way of targeting .NET Standard 1.3). .NET Framework 4.0 is still a target, but we
leverage VS2017 .NET SDK projects to multi-target both net40 and netstandard1.3 to maximize reach and enable libgit2sharp to work across platforms by way of .NET Core.

Closes #1293

[AArnott]

Yes, that makes sense.
nit: I would leave analyzers in PrivateAssets as well, since if analyzers were ever added to the nativebinaries package, it wouldn't be meant to be consumed by libgit2sharp consumers.

[bording]

nit: I would leave analyzers in PrivateAssets as well, since if analyzers were ever added to the nativebinaries package, it wouldn't be meant to be consumed by libgit2sharp consumers.

So my thought process on this was, since we don't have any analyzers in the native binaries package, there wouldn't be any harm dropping that from the list. I can't currently think of a scenario where we'd add an analyzer, but if we did, who's to say if it would be just for LibGit2Sharp, or all consumers?

Ultimately, regardless of which option we choose, there's a chance it would have to be revisited should the native binaries package actually add an analyzer, so it made sense to me to only include things in the list that we know for sure we don't want downstream consumers to see.

[AArnott]

That's fine. It was just a nit anyway, and my motivation for it was to maintain the default nuget include/exclude behaviors unless we had an explicit reason to do otherwise.

[AArnott]

@bording and @ethomson you're not waiting on me, right? I think we're waiting on your review of the PR?
It would be great to get this in, of course. :)

[bording]

@AArnott No, not waiting on you. I do want to take one more look over this now that all the feedback has been incorporated, but I believe the main thing we're waiting on is that @ethomson wants to get out one more release before we merge this in.

[ethomson]

I'd like to do a release but we're waiting on finalizing some things in libgit2. I'm going to branch for the upcoming release so that we can merge this into master.

[Alxandr]

@ethomson Do you have a link to any issue on things being finalized in libgit2?

[stephenwilliams]

Is there any indication when this will be available?

[ethomson]

Okay - v0.24 is released based on libgit2 v0.26. Thanks for your patience.

@AArnott would you mind a final update just to fix the merge conflicts (which I think should be minor, but if not, then please let me know and I'm happy to resolve them), and rev the version number, and then we'll merge this?

[AArnott]

with pleasure...

[AArnott]

Validation complete.

[ethomson]

Thanks @AArnott, @bording and everybody for your hard work and infinite patience! This is amazing! 🎉

[ethomson]

[ethomson]

[ethomson]

[jaredcnance]

This is great and thanks for your work. Any idea when 0.25 will be available on NuGet?

[bording]

@jaredcnance No specific ETA yet, but hoping to have available "Soon".

[Cyberboss]

(tm)