SYNOPSIS:
    MARKC_CUTCUBE x y z toset widthx [widthy] [widthz]

DESCRIPTION:
    Fill the cube/cuboid centered around x,y,z with toset.
    Remarks only voxels that are the same color as x,y,z.
    Doesn't touch greyscale voxels that are protected by an overlay.
    If widthy and/or widthz are not given, they are copied form the
    previous value.
