[Snowball-discuss] Website update update

[Olly Betts]

I've rejigged how the website is updated - this is mostly a "heads up"
in case there's any fallout.

The website "source" is in the snowball/snowball-website git repo.  This
used to require a "generate" script to be run locally and the generated
website was then pushed to the snowball/snowballstem.github.io repo
which would then trigger stuff at github and go live within a few
minutes.

I've eliminated the need for the second repo (and deleted it since it
only contained generated files) and now pushing to the first repo
triggers github actions to run the generate script and push the
generated files to a `gh-pages` branch in that repo, which then goes
live by the same mechanism as before.

As well as being a bit more automated, this eliminates potential for
problems due to having modified files locally.  It also means we can
have CI for proposed changes to the website, but I haven't hooked that
up yet.

The actual update that gets run is exactly the same as before, so
you can still test locally if adding a new algorithm, etc.

There was a short outage yesterday for the website during the switch
over as I had to unconfigure github-pages from the old repo before
configuring the new one.  It should stay up from now on - if the update
process hits an error the website just won't update.

Currently enforcing https (i.e. redirecting http: to https:) doesn't
seem to be working fully, I think it just needs time for github to 
finish processing certificate updates, but https is otherwise working
and we don't process sensitive user data so this seems fairly minor.

The website used to also be served as snowballstem.github.io, but that
no longer works.  I can't really see why it doesn't, but I can find no
evidence that is used anywhere - I think it existing was just a
side-effect of the github-pages implementation.

It appears www.snowballstem.org stopped working at some point (we were
relying on redirection at the registrar), but that now forwards to the
non-www version again (now handled at github).

If you see any other problems please report them.

Cheers,
    Olly