21.7.16: adde/graphics/user-defined painting tools:
. all the painting tools in the graphics editor
come with high-level instructions (adda code)
that users can copy and modify
for coding their own tools.
. your brush can have a parameters page of your own design
not just the usual tool width, flow density, etc.
. each tool is launching a subprogram
that can have any number of novel parameters.
