Give kernel image a header.

Kernel image now has a header with version, magic number, and a
pointer to its actual entrypoint. Entry point is now _start in
boot.s, and we now generate versions.s in the build tree for the
version macros.

src/modules/main/main.c

@@ -1,8 +1,13 @@
-__attribute__((section(".text.entry")))
+#include "vga.h"
+
+void do_the_set_registers();
+
 void kernel_main() {
 	volatile register int foo = 0x1a1b1c10;
 	volatile register int bar = 0;
 
-	while(1)
-		foo = foo | 0xfffffff0 + bar++ | 0xf;
+	terminal_initialize(5);
+	terminal_writestring("YES HELLO THIS IS KERNEL");
+
+	do_the_set_registers();
 }