Add simple implementation of serving directories as zip files

[kimsey0]

This is a first draft of a new functionality that allows downloading the contents of a directory as a zip file. See the issue linked below for why I think this would be useful.

It's implemented using the archiver library, which allows streaming the compressed files directly to the response. There are currently no automated tests, but the feature can be manually tested without any additional setup by running npm start and visiting http://localhost:8080/img.zip.

Questions I'd like answered before I continue the work:

1. Is this something that could fit within the mission for http-server?
2. Are there any concerns about the number or size of the dependencies? archiver adds quite a few transitive dependencies. The number could probably be reduced by using a lower-level library like zip-stream at the cost of more complex wrapping code.
3. How should this be configured? I've currently added a --serve-dir-zip command line argument that controls it. Should it be enabled by default?
4. What happens if there's a zip file with the same name as a directory? Right now, it's served instead of zipping the directory. The risk of collisions could potentially be reduced by serving directory zips at /directory/.zip instead of /directory.zip.
5. Should other archive formats be supported? Support for tar files, optionally gzipped, is included archiver, so it's trivial to enable.
6. And as a last minor question, should a link to the zip file be added to directory listings, and in that case where?

Relevant issues

Fixes #798.

Contributor checklist

• Provide tests for the changes (unless documentation-only)
• Documented any new features, CLI switches, etc. (if applicable)
  • Server --help output
  • README.md
  • doc/http-server.1 (use the same format as other entries)
• The pull request is being made against the master branch

Maintainer checklist

• Assign a version triage tag
• Approve tests if applicable

[kimsey0]

@thornjad, perhaps you can help clear some of these up when you have time and energy? (In any case, thanks for this great utility. 😄)

[kimsey0]

This should probably be case insensitive.

[kimsey0]

@thornjad, any chance you could answer a few of the questions above? 😄

[kimsey0]

@thornjad, any input on whether this could conceivably merge in the right state?

[github-actions]

This pull request has been inactive for 360 days

[kimsey0]

@thornjad, I still think this would be useful. Any chance you think so too?

[github-actions]

This pull request has been inactive for 360 days

[kimsey0]

Still relevant.

[github-actions]

This pull request has been inactive for 360 days

[kimsey0]

Still relevant. Happy to resolve conflicts anytime.