get rid of last remaining lwG
finish gradient
images
pythagorean tree with gradient
line width, first attempt
Hanoi: cycle colors so indexing is not partial

Prompted by an email from Friedrich Wiemer.
small changes to gallery
don't need to install parallel in website builder script
first cut at a section explaining `Measure`
improvements to discussion of line width
remove erroneous claim about default instances for gradient, What to do about defaultLG, and defaultRG either document them or remove them?
write about measurement expressions
add sighting