add iom_peek

Signed-off-by: Hagen Paul Pfeifer <hagen@jauu.net>
add iom_peek() test

Signed-off-by: Hagen Paul Pfeifer <hagen@jauu.net>
add iom_shift comment to explain fuction behaviour

Signed-off-by: Hagen Paul Pfeifer <hagen@jauu.net>