If an error occurs during link checking,
it is important to know where the error occured.
Therefore the request and response objects now contain a the input
source as a field. This makes error tracking easier.
For now we only support JSON.
I honestly don't know if it makes sense to include other formats.
For example, MD and HTML are not really
machine-readable. YAML is not
a great standard format for this use-case. Open for discussions, though.
This splits up the code into a `lib` and a `bin`
to make the runtime usable from other crates.
Co-authored-by: Paweł Romanowski <pawroman@pawroman.dev>
