Use SYS extension for kernel

Makefile

@@ -1,7 +1,7 @@
 FLOPPY = 360
 
 PROGRAMS = $(patsubst %.asm,%.com,$(wildcard programs/*.asm))
-DISTFILES = kernel.com $(PROGRAMS)
+DISTFILES = rdos.sys $(PROGRAMS)
 ROMS =
 
 QEMU_ARCH = $(shell uname -m)
@@ -23,9 +23,9 @@ endif
 
 .PHONY: default clean qemu-rom qemu-floppy
 
-default: kernel.rom
+default: rdos.sys
 
-kernel.com: kernel/*.asm lib/*.asm
+rdos.sys: kernel/*.asm lib/*.asm
 	nasm -s -o $@ -l kernel.lst -I lib -I kernel kernel/main.asm
 
 debug.rom: debug/*.asm lib/*.asm