Version 2.1 with dielectric material

What's Changed

• Update main branch to latest working version by @kakol20 in #13
• Fix normals output by @kakol20 in #14
• Stop use of const reference when not optimal by @kakol20 in #15
• Create PointLight object by @kakol20 in #16
• Add Floyd-Steinberg dithering by @kakol20 in #17
• Normal distribution randomisation by @kakol20 in #18
• Cosine weighted ray by @kakol20 in #19
• Scene class by @kakol20 in #20
• Full scene by @kakol20 in #21
• Dielectric material by @kakol20 in #22
• Change point lights to sphere in full scene by @kakol20 in #23
• Change randomisation of full scene by @kakol20 in #24
• Avoid errors when creating folders that do not exist by @kakol20 in #25

Full Changelog: v2.0...v2.1