TIC-80 tiny computer 0.21.0 dev

version 0.21.0

• you can assign cart cover image by pressing [F7]
• added 'import/export cover' command
• cover loads to screen buffer on every game start
• [github] EXPORT behaves differently on Windows and HTML platforms #64
• [github] Native Scrolling on macOS #67
• [github] Cursor Jump #68
• [github] dofile on first line false detection #65
• [github] Running the MoonScript code using 'dofile' produces an error #70
• [github] Add the ability to run the tic application from the command line with the following parameters: -cart game.tic, -code code.lua #69