errors aren't specific

[orvitpng]

The errors provided, like a missing config, are not good or provided, #6 highlights this problem.

Also, sidenote, the config should be checked at runtime, not compilation.

[Cormanz]

This project is been mostly experimental and I didn't expect this much attention, so a lot of polishing including specific errors are lacking. This is definitely something to fix, so I've pinned it.

The config is checked at runtime, actually. The error for it is just unclear.