v5.4.1

Version 5.4.1: character sets, extend tools, edit_illustration

The README gains sections for generate_character_set,
generate_transparent_character_set, extend_image_set,
extend_character_set and edit_illustration, with example sets for the
two character tools (a rubber-hose cat and a tin wind-up robot).
generate_illustration names its references and edit_illustration;
create_reference routes tokens to each tool's reference parameter and
points set growth to the extend tools; get_generations, edit_image_set
and export_icons match the live descriptions. The plugin descriptions
name character sets and reference images, and the manifests are at
5.4.1.