CLI should have an option for quiet downloads

[danudey]

httpx is a pretty great tool, but one thing I've noticed is that it's (apparently) impossible to use the CLI's download mode to get a progress bar but not show the HTTP response information. An example for when this would be useful is to use in a shell script.

Currently the 'best' way to do this that I know of is to use wget:

wget --quiet --show-progress --progress=bar

This works fine, but in cases where I have httpx (with CLI) installed already (or I'm already installing Python packages into the environment), the httpx progress bar is much nicer.

I can also envision cases where I want to fetch and display (or pipe) the contents of a file to stdout, but again without the extra headers.

What I propose is a CLI flag, --show-headers/--hide-headers, in which:

1. --show-headers is the default behavior
2. --hide-headers prevents the output of response headers in all cases (standard or download mode)
3. Adding ---show-headers after --hide-headers resets the headers display; this is common behavior in other CLI utilities, and is default behavior provided by click.

I have added this functionality in my own fork and added unit tests for the functionality, for both standard and download mode. You can see the commit here:

danudey@f1069d9

I haven't created a PR for this, as the 'Contributing' doc implies that a discussion should happen first, but I'm happy to create the PR if people feel this functionality could be useful.

[lovelydinosaur]

@danudey - This seems valuable to me yep. Thanks for the suggestion.

My inclination here would be supporting a --quiet option, mirroring the existing --verbose option.

(If we want to add --show-headers/--hide-headers then I'd suggest we'd probably also want to be looking comprehensively at all the output that --verbose provides, which seems like a more complex place to start from?)