--- Creates coroutine from function f, returns coroutine.
function create(f)
-- Continues execution of co, returns bool status plus any values.
function resume(co, val1, ...)
--- Returns co status: "running", "suspended" or "dead".
function status(co)
--- Creates coroutine with body f, returns function that resumes co.
function wrap(f)
--- Suspend execution of calling coroutine.
function yield(val1, ...)