mesheets

I am hoping this overall pull request able to receive some attention. In the interim, a comment I would have regarding this pull request is in [build-tool/csproj-template.mtt](https://github.com/HaxeFoundation/hxcs/pull/53/files#diff-68fd34f058bee45599bc3e28bcc1c88aa98f9ea2833cb31e9074e9f19162831d), and specifically around...

Is the added "`-D dotnet_core`" flag intended to deprecate the "`netcore`" and "`netcore-ver`" flags (c.f. [Haxe PR 8391](https://github.com/HaxeFoundation/haxe/pull/8391))? That PR didn't add support for SDK-style project files, though.