Cleanup and restructuring changes

After I just merged three big feature branches (kitty and sixel graphics protocols and the high-res performance branch), I needed to do some overdue cleanup and refactoring. And so I did:

• Collapsed the super long changelog entries into way more readable and legible points

• Restructured the src directory into multiple subdirectories because it had like 50 files already

• Sadly completely removed the Make build system, so now you can only build with CMake (CMake is very much evil and even more evil but it’s the only one of the two that supports windows and I was tired of managing two build systems)

• Removed the –graphics-scale flag, so now everything renders at native resolution

• And some small docs and comment cleanup