No output for `--dump` / Allow to `--dump` extracted links to file

[tooomm]

It looks like the dump flag will not create the expected output.

cat /tmp/lychee/out.md gives No output. Check pipeline run to see if lychee panicked. The dumped output should have the found links, no? 🤔

[mre]

--dump only prints to stdout right now. It does not respect the output file. We should fix probably add support for that. 👍