This new check uses the NPM MarkdownLint package via the NPM MarkdownLint-CLI2 package.

It executes a loose check for consistency and some common errors.
Some of the more annoying rules/rules which could impact display of markdown files on GitHub have been disabled.

All necessary configuration is contained in the `.markdownlint-cli2.yaml` file.

To run locally, install via:
```bash
npm install -g markdownlint-cli2
```
... and then run via:
```bash
markdownlint-cli2
```

Includes a problem matcher which _should_ allow for displaying the results inline in GitHub PR code review view.

Includes adding `node_modules` to the `.gitignore` in case anyone would install these tools locally (to prevent them committing them).

Refs:
* https://github.com/DavidAnson/markdownlint
* https://github.com/DavidAnson/markdownlint-cli2