Migrate to Chirpy

Based on chirpy-starter 00252fd (v7.0.1) with a downgraded html-proofer
to be able to run on "oldstable" Ubuntu 22.04 based systems.

The old index.md has been split into a few "tabs" on the left-hand
sidebar, and two blog post have been added, which are basically the
upstream documentation slightly reformatted.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

Update main body links as well

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>