Merge pull request #108 from libretro/feat/auto-load
A new setting is introduced: "Tape Auto Load" (enabled by default). If disabled, the tape (or disk) will have to be loaded manually, using the ZX Spectrum interface, typically by running LOAD "" (but the method will differ based on the exact model and medium used). To facilitate entering the commands, the virtual keyboard now supports "sticky" shift keys: when a shift key is pressed, the keyboard stays on screen, and a second key can be selected to obtain its "shifted" command or character. If CAPS SHIFT and SYMBOL SHIFT are pressed in sequence, the Spectrum is then in Extended mode, and the virtual keyboard can be used again to enter the extended mode tokens (the green ones above the keys). If a shift key is pressed while in extended mode, the shifted extended mode tokens (the red ones below the keys) are accessible. This is typically useful to use the CAT command (on key 9) to list the contents of disk images.