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.
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>
This implements a basic builder for the Checker struct as discussed in #12.
It is using derive_builder and uses a custom build method to instantiate the more elaborate fields like reqwest::Client.
It also adds deadpool and tokio::mpsc as dependencies to handle a pool of clients to query websites.
