This module collection manages continuations in general, most often
in the form of cooperative threads (also called coros, or simply
"coro" in the documentation). They are similar to kernel threads
but don't (in general) run in parallel at the same time even on SMP
machines. The specific flavor of thread offered by this module also
guarantees you that it will not switch between threads unless
necessary, at easily-identified points in your program, so locking
and parallel access are rarely an issue, making thread programming
much safer and easier than using other thread models.