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
* Sprinkle `const` around where appropriate
- This will make it easier to use `NDS` objects in `const` contexts (e.g. `const` parameters or methods)
* Remove the `const` qualifier on `DSi_DSP::DSPRead16`
- MMIO reads can be non-pure, so this may not be `const` in the future
* Reorganize namespaces
- Most types are now moved into the `melonDS` namespace
- Only good chance to do this for a while, since a big refactor is next
* Fix the build