Add the ':char' syntax for defining character keys with a different
symbol.
This new kind of keys is used to implement Ctrl combinations in the
Serbian Cyrillic layout without showing latin letters while the Ctrl
modifier is activated.

Include comprehensive ctrl modmap, enabling the use of ctrl modifier with Serbian Cyrillic keys. Remove clunky fn modmap previously used for just a few actions such as cut/copy/paste/etc.

Adds Serbian Cyrillic layout. Modmap of Fn key allows for desktop-like easier access to actions such as selectAll, copy, paste, etc. This is because, unlike desktop systems, on mobile ctrl does not combine with cyrillic keys to perform actions.