[racket-dev] [plt] Push #24958: master branch updated

Keep in mind that we were whacked for using 'performance' when we really meant 'optimization'. 

I kind of like the 'tools' idea. I can see that it is too broad (a spell checking tool shouldn't co-habit with a visualizer for futures) but a tools collections with sub-collections for various things sounds good to me:

 tools/
    stepper/
    macro-stepper 
    optimizations/
    future-visualuzation/
    editing/ 

and so on would work.