v0.7.0-int.2

• Introduce .NET Standard 2.1 (.NET Core 3.0) support.
  • Use IAsyncEnumerable<T> from BCL instead of Ix.Async package since .NET Standard 2.1. .NET Standard 1.1/2.0 keeps the original behavior.
  • If you are authoring library on top on this package, make sure you also target .NET Standard 2.1, even if the codebase is the same. This is to keep the dependency correct and prevent IAsyncEnumerable conflict.
• Use Semantic Versioning 2.0.0 for NuGet package versioning.
  • Prerelease package will have an extra "." after "int".