feat: show elapsed and estimated times in console with progress

fix: use float values in sun intensity and rainbow wavelenghts

add pathtracer to examples

feat: small improvements in depth of field, now using 6x6 samples

Update documentation section to README

fix: use scale given by State constructor args

fix: use scale given by State constructor args

feat: normal maps working, refraction not

feat: add solid image texture with parallel projection

refactor: func get_dist for lights, pep8 in main, efficiency in shado…

…w calculation for spotlight