Adapt to Hugo 0.146+

[dscho]

Hugo 0.146.0 overhauled the entire template system. This is likely to break git-scm.com if upgrading blindly (which we do not).

It is probably not quite yet time to upgrade to a newer Hugo (seeing the rapid succession of .1, .2, .3, .4, .5, .6 and .7), but once that stabilizes, we should adapt and upgrade before it gets too much work to adapt the site and upgrade.

[dscho]

There's now also Hugo 0.147.0, .1 and .2, still too fast for my liking. I'd prefer to wait until the templating change dust settles a bit more.

[dscho]

And now there's .3. Still too fast a cadence to let me want to tackle this.

[dscho]

.4 is out; The frequency definitely decreases.