I need --output to be able to specify an output file to write to. At
least, that is the common thing to call it. And also, I was calling the
format "format" already internally and in the docs. I think this is a
bit more logical.
I realized I'm often complaining about tools for not having good
documentation. I tried to get started with D for the Advent of Code
for example, and although it has a reference, I couldn't find good
introductory material. RCL doesn't even have an introduction, so let's
fix that.