Add idt module and set up IDT

src/hulk/gdt.d

@@ -14,10 +14,10 @@ struct gdt
     }
     static assert(gdtr_t.sizeof == 10u);
 
-    private enum size_t SELECTOR_NULL = 0x00u;
-    private enum size_t SELECTOR_KERNEL_CODE = 0x08u;
-    private enum size_t SELECTOR_KERNEL_DATA = 0x10u;
-    private enum size_t SELECTOR_COUNT = 3u;
+    public enum size_t SELECTOR_NULL = 0x00u;
+    public enum size_t SELECTOR_KERNEL_CODE = 0x08u;
+    public enum size_t SELECTOR_KERNEL_DATA = 0x10u;
+    public enum size_t SELECTOR_COUNT = 3u;
 
     static __gshared ulong[SELECTOR_COUNT] gdt;
     static __gshared gdtr_t gdtr;