XKB: Create custom keyboard layouts for X11

XKB layouts are defined by text files living in /etc/X11/xkb/. On some systems they may be placed in /usr/X11R6/lib/X11/xkb/ (on my machine, the later is a symlink to the former directory). There are several subdirectories in that folder, but for the simple task of creating a new layout we are interested only in the symbols subdirectory. Root permissions are necessary for most tasks described below, as all configuration files in this directory are owned by root.