See issue for more details, in general attempting to
implement a coro::thread_pool exposed that the coro::sync_wait
and coro::when_all only worked if the coroutines executed on
that same thread. They should now possibly have the ability
to execute on another thread, to be determined in a later issue.
Fixes#7
Turns out that the final_suspend() method is required
to be std::suspend_always() otherwise the coroutine_handle<>.done()
function will not trigger properly. Refactored the task class
to allow the user to decide if they want to suspend at the beginning
but it now forces a suspend at the end to guarantee that
task.is_ready() will work properly.
