* 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
* First crack at refactoring NDS and DSi into objects
- Remove all global/`static` variables in `NDS` and related classes
- Rely more on virtual dispatch when we need to pick methods at runtime
- Pass `NDS&` or `DSi&` to its constituent components where necessary
- Introduce some headers or move some definitions to break `#include` cycles
* Refactor the frontend to accommodate the core's changes
* Move up `SchedList`'s declaration
- Move it to before the components are initialized so the `map`s inside are initialized
- Fields in C++ are initialized in the order they're declared
* Fix a crash when allocating memory
* Fix JIT-free builds
* Fix GDB-free builds
* Fix Linux builds
- Explicitly qualify some member types in NDS, since they share the same name as their classes
* Remove an unnecessary template argument
- This was causing the build to fail on macOS
* Fix ARM and Android builds
* Rename `Constants.h` to `MemConstants.h`
* Add `NDS::IsRunning()`
* Use an `#include` guard instead of `#pragma once`
* 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
Jesse Talavera