Symmetric coroutines!

test/fiber/call_with_value.wren

@@ -0,0 +1,9 @@
+var fiber = new Fiber {
+  IO.print("fiber")
+}
+
+// The first value passed to the fiber is ignored, since there's no yield call
+// to return it.
+IO.print("before")    // expect: before
+fiber.call("ignored") // expect: fiber
+IO.print("after")     // expect: after