Windows/macOS: Update SDL2 to version 2.0.16

Pushed v1.47 code (mega-commit, unfortunately)

Fixed problem loading audio settings from config in v1.45

Pushed v1.45 code

- Fixed possible crash when starting the program on M1 Macs (thanks kode54)
- Fixed possible mouse cursor corruption when hovering over text boxes on Linux
- Fixed possibly buggy string operations
- Refactored some code that was doing unnecessary/wrong stuff
- Minor code cleanup
- Updated help text

VS project file: How on earth did you end up in there?

Add new src folders to CMakeList.txt (issue 8bitbubsy#16)

Don't cache scrollbar parameters (caused stupid bugs)

Remove SD_RENDERER_ACCELERATED flag (fixes problems in rare cases)

Delete test.zip

Linux compile fix