Add serial module

src/hulk/hulk.d

@@ -21,6 +21,7 @@ import hulk.pic;
 import hulk.acpi;
 import hulk.apic;
 import hulk.rtc;
+import hulk.serial;
 
 extern extern(C) __gshared ubyte _hulk_bss_size;
 
@@ -56,6 +57,7 @@ void hulk_start()
 {
     cli();
     initialize_cpu();
+    Serial.initialize();
     Gdt.initialize();
     Idt.initialize();
     Fb.initialize(cast(uint *)Hurl.HULK_FRAMEBUFFER,