Functionality/optimizations

Better memory manage (smart pointers, vector instead of list)
Extract all random number generations to a class so that seeding and initializing is done just once
Add motion blur
Add Bounding Volume Hierarchies
- Add random axis sorting of boxed hittables
- Study the possibility of a better choice of axis w.r.t. which we do the spacial ordering at each step
Try to switch to constexpr as much as possible
Use timing tool to find out if constexpr is helping
Add the option to check if the new plemma::glancy::Hittable would invade other plemma::glancy::Hittables in plemma::glancy::HittableList::Add()
Parallelize
In axes_aligned_bounding_box.hpp, if Minima() and Maxima() return Vec3 instead of Vec3 const& the tests in hittables_test take much longer to finish (and will possibly be red). Study that case and see possible changes around glancy.

Tools

Add timing tool:
- class plemma::chronometer::SingleMeasurement
- free method plemma::crhonometer::MeasureFunction()
Add image visualizer (i.e., open the image on a window when done)

Add image.h
Rework to add scenes and renderer
Switch to use uint8_t, uin16_t, etc
Improve use of namespaces
Check that naming conventions are preserved (as of Google's style guide or whichever is decided)
Add automatic formatting

Property-based testing seems a good approach, Catch2 still doesn't fully support property-based testing, but generators might provide a good start: https://github.com/catchorg/Catch2/blob/master/docs/generators.md