Add GPL-2-or-later license headers to the DOS utility source files and
document the purpose and local dependencies of each C, header and assembler
file.
Preserve the original Martin Stover copyright attribution for the historic
MARS-NWE utility sources, including files that did not previously carry an
explicit header but are part of the original tool set. Add Mario Fetka as the
2026 copyright holder for the current maintenance work, and use Mario-only
headers for files without original Martin Stover ownership.
Also add a root-level COPYING file containing the GPL-2 license text.
