wip: Upgrade to jekyll 4

_posts/2015-08-19-foss-failmeter.md

@@ -13,7 +13,7 @@ I have recently bumped into [this
 article](http://spot.livejournal.com/308370.html). Naturally, I quickly
 calculated the FAIL metrics for all my projects (most of them are pretty high).
 To ease calculation, I made up a
-[small page]({{ '/failmeter/' | prepend: site.baseurl }}) based on this list
+[small page]({% link failmeter/index.html %}) based on this list
 (although I have divided the points by 5; I really don’t understand why spot is
 using such big points if all of them can be divided by 5). Feel free to use it,
 and if you have any recommendations (point additions/removal, new categories,

_posts/2016-09-28-emacs-package-to-generate-gobject-boilerplate.md

@@ -30,7 +30,7 @@ it felt to be a really poor experience, especially given that I made
 my feet wet with Emacs Lisp. So I dug deeper, and created a package
 for that.
 
-![A screenshot of GobGen in action]({{ site_url }}/images/screenshot-gobgen.png)
+![A screenshot of GobGen in action]({% link images/screenshot-gobgen.png %})
 
 GobGen has its own buffer with some widgets, a bit similar to
 `customize`. You can enter the name of your new object and its parent,

_posts/2016-11-03-how-i-started-with-emacs.md

@@ -34,16 +34,16 @@ fan of Nyan cat (did you know there is even a site
 called [nyan.cat](http://nyan.cat/)?) and since then I have it in my
 mode line:
 
-![Nyan modeline]({{ site_url }}/images/nyan-modeline.png)
+![Nyan modeline]({% link images/nyan-modeline.png %})
 
 …in my `eshell` prompt:
 
-![IMAGE HERE]({{ site_url }}/images/nyan-eshell.png)
+![eshell prompt with a Nyan cat]({% link images/nyan-eshell.png %})
 
 …and I also [zone out](https://www.emacswiki.org/emacs/ZoneMode) with
 Nyan cat:
 
-![IMAGE HERE]({{ site_url }}/images/nyan-zone.png)
+![a text-based animation with Nyan cat]({% link images/nyan-zone.png %})
 
 Now on to more serious stuff. After browsing through all the packages
 provided by [ELPA](http://elpa.gnu.org/), I found tons of useful (and