Error on parse

[ProbablyClem]

Depends on : this pr
It's a really small change but the diff is big because the refacto branch as not been merged yet

Panics if a file is not found/cannot be found

Currently, if a file doesn't exists, you get no warning at all.... which is very dangerous.

It's hard to spell the file name right cause there's no autocompletion so we need at least this safety guard

[rxdiscovery]

Hello,
It's good to have thought about error handling, when I developed this crate, it was to solve an urgent problem, I didn't have time to refine it, anyway if there's an error it will happen at the build process level and will never impact the final program.
But we still need good error handling, thank you very much.