Cleanup. Added files. The written image boots ok! Tested on Debian only.

Script file cleanup.

The script file runs ok on Debian 7.6. The written image boots into
FreeDOS. AUTOEXEC.BAT and CONFIG.SYS were included into the overlay/
directory.

syslinux.cfg is configure to boot memtest86+, Odin 0.6 and 0.7 image
files. Just copy those files into overlay/boot/.