Migrated to .NET Core 3.0

Migrated to .NET Core 3.0

Breaking Changes

• TasksExtensions moved from the System namespace to the System.Threading.Tasks namespace
• Threaded.Threaded* classes have been renamed to Threaded.*
• Threaded.ContextItemCollectionFactory now throws NotSupportedException in-place of using an inappropriate collection.
• Cache support has been removed for .NET Core.