Lint JavaScript in Pug by providing eslint interface

[ezhlobo]

Initial request: #61

Interface

{
  rules: {
    'react-pug/eslint': ['error', {
      // Rules from eslint, these two for instance:
      'no-multi-spaces': 'error',
      'indent': ['error', 2],
    }],
  }
}

Checklist

• Allow running eslint for JavaScript in Pug
• Improve LOCs in reports