New @-codes: GETKEY and WAIT:<milliseconds>

GETKEY waits indefinitely for any key press by the user (resolves issue #245).
WAIT:<n> waits for up to n-milliseconds for a key press and then continues on.

For both cases, the key pressed is not echoed or acted upon in any way. Ctrl-keys could be handled by global or built-in ctrl-key handlers, so those would be the exception.