DOS tool to unpack disk image

Here is little DOS (or Windows dosbox) tool to unpack FAT12 disk image file

Usage:
  unimg disk.img

It will create subdir (=filename without extension) and unpack
full directory structure with all files and subdirs to HD.

Notes:
 - only FAT12 with DOS like 8.3 names supported
 - image file need file extension
   (filename first 8 chars is used by dir name)
 - use only normal DOS file functions
