Kernel: Use a multiboot header instead of a convoluted two-part bootloader.

The old bootloader was hilariously complicated, requiring a floppy disk with
the kernel on it, and a hard drive with the file system. This patch removes
the floppy disk from the equation and replaces it with a multiboot header.
This means the kernel can now be booted with qemu-system-i386 -kernel kernel

Kernel/init.cpp

@@ -136,7 +136,7 @@ VFS* vfs;
     ASSERT_NOT_REACHED();
 }
 
-[[noreturn]] void init()
+extern "C" [[noreturn]] void init()
 {
     cli();