Some more suspicious swapchain RFC keyword usage

I notice some more suspicious swapchain RFC keyword usage:

> The possible return values for `vkGetSwapchainStatusKHR` **should** be interpreted as follows:

The "should" feels odd here and colloquial. Should be refrazed in the form of what the implementation **must** return.

> If a counter is not available because the swapchain is out of date, the implementation **may** return `VK_ERROR_OUT_OF_DATE_KHR`.

"may" feels suspicious here. Posibly supposed to be "must".

> As usual, `vkQueuePresentKHR` **may** fail if `oldSwapchain` has entered a state that causes `VK_ERROR_OUT_OF_DATE_KHR` to be returned.

The "may" is weird, because tautologically if `VK_ERROR_OUT_OF_DATE_KHR` is returned, then it did fail.