lts-doc: sort documentation alphabetically

As a follow up to #3651 (closed), and to #393 (closed), I've started from the top and am working my way down.

This is a WIP! Against v4.x!

I am posting this now because it is a big diff and will need eyes.

Docs that have been completed:

• assert
• buffer
• child_process
• cluster
• console
• crypto
• dns
• filling in as I go

Help is more than welcome!