Upgrade Target Framework version

[kagikn]

About the v3 branch, upgrading Target Framework version won't be problem because we haven't even released the first version and we don't need to worry about any breaking changes. And I believe upgrading it for the v2 branch won't be problem.

I tested which framework version .NET scripts for v2 are running on with this code

var cal = new PersianCalendar();
UI.ShowSubtitle(cal.MinSupportedDateTime.ToLongDateString());

The result is March 22, 0622 or a equivalent value when you have .NET Framework 4.6 or greater. Therefore, we can say SHVDN and their scripts are running in what .NET Framework version you have, and we don't have to worry about the framework compatibility. Upgrading Target Framework version doesn't break any existing scripts compatibility. We can also use some cool features such as ValueTuple by upgrading Target Framework version (not useful as it is in C# projects with VS2017 tho).

Also, would you consider upgrading Windows SDK version to 10.0.17763.0 and minimum Platform Toolset version to v141? @crosire

[crosire]

I don't mind. It shouldn't break any scripts, so sure, why not.

[kagikn]

@crosire I couldn't change the AppVeyor configuration because there isn't appveyor.yml at the root of the repo, so please export and commit it to let me change the AppVeyor config when it needs to be changed in the future.
This time, add image: Visual Studio 2017 and add /p:WindowsTargetPlatformVersion=10.0.17763.0 as a msbuild parameter, and we should be able to test commits.