Restructure kernel to use 1-segment COM convention

Makefile

@@ -1,5 +1,5 @@
 PROGRAMS = hello.com
-DISTFILES = kernel.bs $(PROGRAMS)
+DISTFILES = @rdos.com $(PROGRAMS)
 ROMS =
 
 QEMU = qemu-system-i386
@@ -43,7 +43,7 @@ host/%.elf: host/%.c
 %.bs: boot/%.asm
 	$(NASM) $(NASM_ARGS) -o $@ $<
 
-kernel.bs: kernel/*.asm
+@rdos.com: kernel/*.asm
 
 # Special case: variations of FAT vbr
 fat1.bs: boot/fat.asm
@@ -62,7 +62,7 @@ fat6.bs: boot/fat.asm
 fd%.img: $(DISTFILES) $(SYS)
 	mformat -C -i $@ -f $* -c 2 -v "$(LABEL)" ::
 	mcopy      -i $@ $(DISTFILES) ::
-	$(SYS)        $@ hello.com
+	$(SYS)        $@ @rdos.com
 
 clean:
 	rm -f *.com *.bs *.0 *.lst *.img *.bin *.rom