TST: test sphinx-reredirect

[mmcky]

This PR tests infrastructure for linking old lectures to the new reorg structure

[github-actions]

🚀 Deployed on https://657acbe5a8f4d87f3d0a8ff0--nostalgic-wright-5fa355.netlify.app

[mmcky]

@HumphreyYang we will need to use sphinx-reredirects to achieve our external redirections.

It is pretty simple syntax so not sure if you want to auto-generate as part of your scripts that we can use after the reorg lecture sites are live. It will be pretty simple to deploy by adding

<filename>: <url> 

to the _config.yml.

such as

heavy_tails: https://intro.quantecon.org/heavy_tails.html

Note: no need for an extension here