Improving the usability of Fontus

[leeN]

I'm aware that the usability of Fontus is fairly lackluster, partly due to it solving a difficult problem but also due to us not putting in all that much effort in this area.

This issue serves as a tracking issue to track general progress on improvements here.

This can include:

• Improving the documentation. I'm not quite sure how approachable it is, but there are probably some very low-hanging fruits in this area.
• Adding some basic validation, i.e., catching obvious mistakes early and avoiding the user having to fuzz the config until it works.
• A basic application and a tutorial on how to write a Fontus config.
• More suggestions are welcome!