Coroutines TS and Coroutine Task Type

The coroutine function of arkio requires C++20 coroutines ts. However, the original technical standard alone is not enough for writing nested coroutines, and would normally require libraries like cppcoro() to provide aiding classes and functions.

This library does not use cppcoro, however, but implemented a set of tools introduced in another paper, p1056r0(http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p1056r0.html) to support coroutine nesting and spawning, for details, see ark::task and ark::co_async

For complete examples on how to write coroutine programs with arkio, see:

• coro_echo_server.cpp
• coro_cat.cpp