Stackless resumable functions

[Kagamin via Digitalmars-d]

In my experience with .net, async/await introduce a non-obvious 
multithreading model, which remaining hidden under the hood, can 
still inflict concurrency issues on your code: race conditions 
and deadlocks. And while C++ and C# don't know about shared 
types, D will need to catch concurrent access to data, as it's 
required by D type system.