Only use Hash task on VS 2019 and higher. (microsoft#763)

Remove /await flag for compat with C++20 (microsoft#756)

C++20 coroutine support (microsoft#748)

Allow cancellation to be propagated to child coroutines (microsoft#721)

Make vector<bool> work again (microsoft#703)

Add multi-threaded collections (microsoft#692)

Fix build

Fix concat_hstring for 0-length string (microsoft#675)

Fix concat_hstring for 0-length string (microsoft#675)

Resuming neutral context from STA should force background thread (mic…

…rosoft#662)