Finally had the chance to rewrite "highcal" in C.

<https://uninformativ.de/git/highcal>

It's a little program that prints calendars, much like cal(1), but uses
more colors and can highlight dates fed to it via stdin.

highcal used to be part of gitodo:

<https://www.uninformativ.de/git/gitodo/file/highcal.html>

gitodo and highcal were Ruby scripts. Ruby was an experiment at the end
of 2012. The language looked nice, but I have not gotten used to it.

gitodo itself has already been replaced by the much simpler "be":

<https://www.uninformativ.de/git/bin-pub/file/be.html>

So, no more Ruby for me. Phew.