Overhaul development and test dependencies.

[matthewmcvickar]

This is an attempt to simplify and update the dependencies for this project.

There are a few reasons for this:

• The GitHub workflow for testing that runs on each push is failing because the package dependencies are out of date.
• The JavaScript testing framework nodeunit has not been under active development for a long time and has numerous security vulnerabilities.
• The development tooling workflow library Grunt has not been under active development for some time and has numerous security vulnerabilities. It is also unnecessary, as the same functionality can be replicated by using NPM scripts defined in package.json.

What was done:

• Removed Grunt. Replaced its functionality with NPM scripts in package.json.
• Removed nodeunit. Replaced it with the Jest JavaScript testing framework and updated the tests accordingly.
• Removed jsonlint. Replaced it with @prantlf/jsonlint, a fork of jsonlint that is improved and actively maintained.
• Updated JSHint.
• Updated README to replace mention of Grunt with an example of how to run Javascript tests.
• Update GitHub Actions workflow YAML to reflect new JS testing.

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I have a few other PRs in the hopper for this project, but I wanted to get the baseline dependencies updated and automated tests working before going any further.