Major restructuring of SlimEngine++ : https://github.com/HardCoreCodin/SlimEngineCpp

• Much more opt-in/pay-for-what-you-use as opposed to batteries-included
• Scene, Selection, Viewport and Hud now need to be instantiated explicitly (if/as needed)
• 'draw(*)' now free functions (exp. included for non-single-header variant per-drawable)
• 'mouse' is now a global namespace (instead of a struct instance, like 'os::')
• No more global 'settings::' namespace (memory isn't pre-allocated automagically)
• No more global 'memory::' namespace (monotonic-allocator is now opt-in)
• Transform and Camera orientation structs improved
• obj2mesh CLI improved (added scaling and rotation arguments)
• All example apps rewritten and tested with both single-header and lib variants
• README.md updated with new code screenshots showing the new API use