Nighty-night Nightlys :(

• Migrate from .NET Core 3.1 to .NET 6.0 (LTS).
• Due to (new?) AppVeyor restrictions of 1024 MB/day bandwidth on Artifact downloads, the auto download feature had to be removed.
• Removed the dependency on Newtonsoft.Json, no longer required after removing the auto-download.
• Installation instructions have been completely rewritten to make it much more clear.
• Thanks Mateo Carriqui (system32uwu) for taking the time to fix a small width and height safety check mistake. (#5, #6)