The `sleep()` function pauses program execution for the given amount of
milliseconds.

Returns `true` if the program slept.

Returns `false` when the given time value was not convertible to an integer,
negative or zero.

-- Testcase --
{%
	let t1 = time();

	sleep(1000);

	let t2 = time();

	printf("Slept for %d second(s).\n", t2 - t1);
%}
-- End --

-- Expect stdout --
Slept for 1 second(s).
-- End --


Passing an invalid value yields `false`.

-- Testcase --
{%
	printf("%.J\n", [
		sleep("inval"),
		sleep([]),
		sleep(-1),
		sleep(0)
	]);
%}
-- End --

-- Expect stdout --
[
	false,
	false,
	false,
	false
]
-- End --