Add timeouts to net functions.

Further debugging of the general timeout system, as well
as having a single fiber wait on multiple state machines (select).

src/core/fiber.c

@@ -81,6 +81,7 @@ JanetFiber *janet_fiber_reset(JanetFiber *fiber, JanetFunction *callee, int32_t
     }
     if (janet_fiber_funcframe(fiber, callee)) return NULL;
     janet_fiber_frame(fiber)->flags |= JANET_STACKFRAME_ENTRANCE;
+    fiber->waiting = NULL;
     return fiber;
 }