Add initial HOS EFI Loader sources

src/hel/hel.d

@@ -0,0 +1,17 @@
+import uefi;
+
+extern (C) EFI_STATUS efi_main(EFI_HANDLE image_handle, EFI_SYSTEM_TABLE * st)
+{
+    st.ConOut.ClearScreen(st.ConOut);
+
+    st.ConOut.OutputString(st.ConOut, cast(CHAR16 *)"HOS EFI loader\r\n"w);
+    st.ConOut.OutputString(st.ConOut, cast(CHAR16 *)"Press any key...\r\n"w);
+
+    st.ConIn.Reset(st.ConIn, FALSE);
+    EFI_INPUT_KEY key;
+    while (st.ConIn.ReadKeyStroke(st.ConIn, &key) == EFI_NOT_READY)
+    {
+    }
+
+    return EFI_SUCCESS;
+}