Add: working serial port output driver

kmain.c

@@ -5,6 +5,9 @@ int kmain(int retvalue)
 {
   clear();
   puts("hello\nbrave\nnew\nworld");
-  serial_write("hello", 1);
+
+  init_serial();
+  serial_puts("Hello, brave new world. This is a message to let you know that the kernel has started.\n");
+  serial_puts("This is a second message.\n");
   return retvalue;
 }