Rename LICENSE to COPYING

Signed-off-by: Christophe Vu-Brugier <cvubrugier@yahoo.fr>
Add target-export-device; it exports a block device as an iSCSI target

Signed-off-by: Christophe Vu-Brugier <cvubrugier@yahoo.fr>
Describe target-export-device in README.md

Signed-off-by: Christophe Vu-Brugier <cvubrugier@yahoo.fr>