Added, Linedef Edit window: added "Replace unused textures" checkbox. When disabled, textures on unused sidedef parts won't be replaced when changing textures. For example, you can now replace sidedef textures of the whole map at once without assigning middle textures to all double-sided sidedefs.
Updated documentation ("Compiling GZDoom Builder" - added "Quick start guide" section).
Updated ZDoom_DECORATE.cfg.