Add `nwis_client` CLI

[jarq6c]

This PR adds a minimal command-line interface to the nwis_client subpackage. The CLI entry point is called nwis-client. The nwis_client README includes examples of use. Currently the tool generates a CSV based on an arbitrary number of USGS site codes (see usage/help output in README). It includes three optional parameters: --startDT, --endDT, and --parameterCd. @aaraney

Additions

• cli.py

Removals

-

Changes

• value_time_label now defaults to value_time per #117
• escalates warning to exception per #160

Testing

1. Added minimal testing for CLI. Note: click includes test funtionality per CLIRunner, but this did not play well with asyncio, so I implemented similar functionality using subprocess.

Notes

• Closes #117
• Closes #35

Todos

-

Checklist

• [x] PR has an informative and human-readable title
• [x] PR is well outlined and documented. See #12 for an example
• [x] Changes are limited to a single goal (no scope creep)
• [x] Code can be automatically merged (no conflicts)
• [x] Code follows project standards (see CONTRIBUTING.md)
• [x] Passes all existing automated tests
• [x] Any change in functionality is tested
• [x] New functions are documented (with a description, list of inputs, and expected output) using numpy docstring formatting
• [ ] Placeholder code is flagged / future todos are captured in comments
• [x] Reviewers requested with the Reviewers tool :arrow_right:

[jarq6c]

@aaraney I'm unable to add you as a reviewer until you comment. Any feedback you want to give?

[aaraney]

@jarq6c, thanks for pinging me. Id seen this, but had not had a chance to take a look. I certainly want to give you feedback / a review -- let me go ahead and do that now.

[jarq6c]

This has been published to PyPI.