Update README and file-level comments after the NCP/IPX source split and
renames.
Document the current layering: ncpapi.c/ncpapi.h contain the ncpXX_YY_*
protocol API wrappers, ncpcall.c contains low-level requester/transport
helpers, ncp.asm/ncp.h provide INT 21h and Client32 requester entry points, and
ipx.asm/ipx.h provide IPX and far-memory assembly glue.
Also remove stale c32ncp/kern_wasm/kern.h planning references and update the
license section to mention the root-level COPYING file.
No behavior change.
Finish the c32ncp.c/c32ncp.h to ncpapi.c/ncpapi.h rename.
Update the build files, include directives, dependency tracking, header guard,
README references and file-level comments to use the new ncpapi naming. This
matches the current split where ncpapi contains the ncpXX_YY_* protocol API
wrappers and ncpcall contains the lower-level requester/transport helpers.
No behavior change.
