Change return value of docs:byeach

Change return value of docs:byeach

Rather than 0 for continue and non-zero for stop,
use Efalse for don't continue, Errors for abort,
and normal values for continue.

This makes it similar to event handlers which stop being called after
Efalse.

Also cause a False return from python code to be Efalse.

Signed-off-by: NeilBrown <neil@brown.name>