v6.0.0

Version 6.0.0: illustration sets, edit_set and export_set

The README's tools half is regrouped for the 6.0.0 tool set: making a
set (generate_image_set on a color or transparent,
generate_character_set, generate_illustration_set), growing one (the
three extend tools), delivering one again (edit_set, export_set),
references, and generations and credits. Its examples are new sets
shown from export_set; the old example images are removed.

The manifests are at 6.0.0 with a description and keywords that name
the three kinds of set.