.extract file [+off][-off][len]
 [-f] [-o outfile] [-a outfile]
 [-m address]

input:
  file = input filename
  +off = byte offset from start
  -off = byte offset from end
   len = length in bytes

output:
  -f  = overwrite permitted
  -o  = write to output file
  -a  = append to output file
  -m  = copy to 64k mem address

no -o,-a,-m generates hexdump

extract v1.1 spectrum z88dk.org
