Log Message:
x11/XaoS: update to version 4.2.1.

Lots of changes, the biggest of which is that it now uses Qt5 as GUI toolkit.

4.2

New Features

    Palette editor, save/load palettes, storing user palettes in the .xpf file.
    The option 'User formulas' maintains a history of recently used formulas.
    Fractal info in the Help menu.
    Batch rendering.
    Enabled panning in rotate mode.
    Unified Open and Open Image option. Save Image option moved to Save as.

4.1

New Features

    Added option to show Cartesian coordinate grid.
    Custom palette helps visualizing palette before applying changes through \ 
slider selectable values now.
    PNGs exported using 'Save Image' option can be imported back and users can \ 
continue zooming on it.

4.0

What's new in 4.0

    The user interface is based on Qt, so XaoS has a modern look and feel.
    Works on macOS Catalina, which broke older versions.
    Animation rendering has been fixed.
    Menu entries are now standardized.
    TrueType text rendering so fonts look nicer and non-Latin alphabets are \ 
supported.
    Hindi, Icelandic, Russian, Serbian and Swedish translations.
    Several minor updates for the other languages.
    The language can be set in the View menu now.
    Lots of bug fixes.
    Zooming is possible also with the mouse wheel.
    Mouse cursor has been changed to cross.
    Iteration number N can be used in user formulas.
    Lots of source code cleanup and refactoring. It may not be obvious to end \ 
users but this will allow us to make better features and more frequent releases \ 
in the future.

3.7

There were quite a few bug fixes at this point since 3.6 was released.