doc: improve consistency in documentation titles

Unify capitalization and spaces and add some info for consistency,
clarity and coherence with sorting in the all.md / _toc.md.

PR-URL: https://github.com/nodejs/node/pull/11230


Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>
Reviewed-By: Timothy Gu <timothygu99@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>