Introduce tool to customize cursor pixmaps

[jouae]

One of the features of MADO is the ability to use a cursor, which can be enabled in the configuration settings.

The cursor functions and window update processes are defined in screen.c and cursor.c. In particular, cursor.c uses a $20\times64$ array named _twin_cursor_default as input for twin_pixmap_create_const, which generates a default white cursor similar to the one in the Windows system.

A custom cursor tool, such as cursor-toolbox, can be created under the tools directory to provide more diverse cursor options.

see https://github.com/charakterziffer/cursor-toolbox