Enhances `Makefile` to make build dependencies self documenting.
Enhances `Makefile` to make build dependencies self documenting.

- All build tasks requiring `npm` dependencies depend on `node_modules`
  target.
- `node_modules` file/directory target depends on `package.json` and
  `dist/*/*.min.js` files. Person building can never forget a step.
- Use the variable `$(RM)`.

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