Window system added/re-worked (nearly non-existant earlier)
- Support for multiple windows nearly working.
- Rendering restructured
- Application defaults moved to own namespace.
- Viewport and RenderViewport classes merged
- Public functions have been added to access the top and main windows.
- Public functions have been added to access the active, global and relevant UIs.
- Window system moved from OS to own Window folder.
- WndProc and XProc moved to Window folder for coherency