Take dd a bit further: if= and of=
Take dd a bit further: if= and of=

argument handling is a bit odd but basically we transform old school
if= to -if arg and let flag.Parse do the rest.

Signed-off-by: Ronald G. Minnich <f569d0af9a3481c4007b95c7180d6c41009f2513@gmail.com>

rminnich/u-root,hugelgupf/u-root,u-root/u-root,GanShun/u-root,rminnich/u-root,GanShun/u-root,rminnich/u-root,u-root/u-root,hugelgupf/u-root,hugelgupf/u-root,hugelgupf/u-root,u-root/u-root,GanShun/u-root,rminnich/u-root