#493 elfcopy: implement -i and --interleave-width

[Ed Maste]

from the GNU objcopy man page:

       -i interleave
       --interleave=interleave
           Only copy one out of every interleave bytes.  Select which byte to
           copy with the -b or --byte option.  The default is 4.  objcopy
           ignores this option if you do not specify either -b or --byte.