Multi-instrument mode (uke, banjo, 7-string), settings filee

Added support for variable number of strings, plus the application stores some settings in fretboard_settings.json. Here, you can e.g. set your instrument up as an ukulele, a banjo or a 7-string guitar with the tuning and title of your choice.

Better help, refactoring, comments, icons

1.2

Icons.

More functional hotkeys, click to transparent

v1.1

Update README.md

Initial binary release

Binaries built on Windows 11 and Ubuntu 24.04.