Set up a sockets demo for contrast about revolving-doors

[robertdfrench]

This will help make the speed case as laid out here https://github.com/robertdfrench/revolving-door/tree/master/C0_door_bandwidth

[robertdfrench]

Maybe even just drop this and cite the Stevens book to claim doors are faster. Or don't even bother. But this is sortof going astray from "how to use it" and veering more into "why to use it" and I think that can be expanded over time.

[robertdfrench]

Definitely not going to pursue this.

[robertdfrench]

This works and it's neat, so it's worth formalizing and showing off

[robertdfrench]

Added in cd5b25a