Create a proof of concept for html-slim in the makefile

[willingc]

🧰 Task

I would love a superfast build of the docs that is even faster than the options that we have today. If I am making a page change unrelated to gallery/examples/api, I would love a dev build called html-slim that builds in under a minute. I kludged up something on my fork so I can do this but it's not suitable for production as I stripped out a bunch of files. I'm noodling over if we can use conditionals to accomplish something similar.