Add manpages for isohybrid, memdiskfind

Signed-off-by: Peter Jones <pjones@redhat.com>
isohybrid: Improve help/man

Signed-off-by: Gene Cumm <gene.cumm@gmail.com>
Merge branch 'syslinux-4.xx' into syslinux-5.xx
Merge branch 'syslinux-5.xx'