Put result on standard out if no --output option specified?

This is how curl works. This would be a nice-to-have addition because this way you can do things like:

```
dp2 results --zipped myjob | unzip
```

This is a lame example because you can accomplish exactly the same with `dp2 results myjob`. But if the CLI would support downloading single files, not only ZIPs, it would open up more useful possibilities.

What's not so nice is that when you accidentally forget the --output argument you get a lot of output in your terminal, and in case of a ZIP, a lot of binary output. So maybe a better idea would be to do it the wget way, namely support `-` as your output file:

```
dp2 results --zipped --output - myjob
```

Currently this simply creates a ZIP file named "-". With the desired behavior the `--zipped` argument becomes redundant.

Start at the CLI entry point for `dp2 results` and trace handling of `--output`, `--zipped`, and the `-` filename. The issue presents alternative behaviors, so confirm the intended choice before implementation; completion should match that choice for the command examples and avoid unintended terminal output.

Written by the indexing model from the issue text.