Update links to use folders rather than .html

[choldgraf]

This updates our link generation so that pages use folder names instead of pagename.html convention. This is more common in modern website workflows, and leads to more memorable URLs. It is also going to be the default behavior in Jupyter Book 2.

So for example:

• Old: https://jupyter.org/governance/list_of_standing_committees_and_working_groups.html
• This PR: https://jupyter.org/governance/list_of_standing_committees_and_working_groups

This will break any pre-existing direct URLs to our governance docs, but it's also a more future-proof decision that we'll only need to make once.

Suggest we hold off until #266 (comment) is resolve or deemed impossible

[fperez]

Is there any possibility to create automatic redirects? I don't know enough of the details on redirects for sites hosted on gh-pages as ours, so if it's a major pain, I guess we can live with the breakage. But there's bound to be links lying around on various issues, discussions and online messages, so it would be nice to avoid breaking things if it's not too difficult.

[choldgraf]

Now that you mention it, I wonder if this is something we can add to MySTMD to support JB1 upgrade pathways. If so, then we could hold off on making this change now and use the upgrade functionality in JB2 when it is released. I created an issue to track that here:

• [JB1 upgrade] Add option to create redirects from .html pages to page/index.html jupyter-book/jupyter-book#2328

We don't have any resources for that project right now, so any cycles from folks that are interested in helping with that would be most welcome!

[fperez]

That sounds like a great idea!