merge doublemelon (#2067)

non-exhaustive (but exhausting) list of changes:

* base laid for multiple window support, but will likely require more work to work correctly
* encapsulation of frontend state for proper multi-instance support
* (JIT still needs a fix for the NDS::Current workaround but we can get there later)
* new, more flexible configuration system

src/DSi.cpp

@@ -70,8 +70,28 @@ const u32 NDMAModes[] =
     0xFF, // wifi / GBA cart slot (TODO)
 };
 
-DSi::DSi(DSiArgs&& args) noexcept :
-    NDS(std::move(args), 1),
+/*DSi::DSi() noexcept :
+    DSi(
+        DSiArgs {
+            NDSArgs {
+                nullptr,
+                nullptr,
+                bios_arm9_bin,
+                bios_arm7_bin,
+                Firmware(0),
+            },
+            nullptr,
+            nullptr,
+            nullptr,
+            nullptr,
+            false
+        }
+    )
+{
+}*/
+
+DSi::DSi(DSiArgs&& args, void* userdata) noexcept :
+    NDS(std::move(args), 1, userdata),
     NDMAs {
         DSi_NDMA(0, 0, *this),
         DSi_NDMA(0, 1, *this),