Demo 2: Fixing an Issue, Adding a new Feature

demo-01.index.html has the output of a former run of ../demo1
There is an issue where the background flickers as the last few particles fade out. Smooth out the rapid color change.
Add a new feature: clicking should cause a burst of particles as well as a shift in the overall hue.
The output of a previous plan is in old-plan.md.
These tasks can also be found as issues in the corresponding Git repository: #1 and #2.