* Add extension to ESLint config file
The .eslintrc file without an extension was deprecated a few years ago,
so this change renames the file to add the required extension.
See: https://github.com/eslint/eslint/commit/c9a8883d450d63a8d044a9e66d275f5b1973a3ba
* Add ESLint to package.json
This change adds ESLint as a dev-dependency and adds a lint script that
will run ESLint.
* Complete switch from JSHint to ESLint
Convert all the JSHint rules to the ESLint equivalents where possible.
The no-undef rule in ESLint caught a few cases of undefined usages in
the tests, so they were also fixed.
* Add a .eslintignore file
The HTML coverage report is currently being linted, which causes a lot
if invalid linting errors. This change adds a ignore file to ensure these
files are properly skipped during linting.
