eslint-index

I have created a ESLint utility module inspired by `eslint-find-rules` that I thought you might find useful for `eslint-config-airbnb-base` and `eslint-config-airbnb`.

The module is called `eslint-index` and you can [read the full documentation on npm](https://www.npmjs.com/package/eslint-index).

`eslint-index` provides a great deal of functionality including:
* List all available rules declared by ESLint and any plugins you have included
* Colour code rules depending on their status:
* `omitted` (not declared anywhere in you ESLint config file)
* `0|off` (declared, but set to `0|off`)
* `1|warn`
* `2|error`
* Display links to the rule documentation page next to each rule
* Filter/reject rules by their `status` and/or their `group`
* `status` is as described above (`omitted|off|warn|error`)
* `group` is `eslint` for the core ESLint rules _or_ the name of any of your plugins like `react|import|flowtype`
* Format the output as a number or a table to get an overview of your rule settings
* Rules that have been marked as deprecated are removed from all outputs
* All of the above filters and formatting can be combined, for example:
* `filter` `omitted` and `off` rules, output them as a `list` and display the rule `doc` links alongside
* `filter` `eslint` rules and display the rule setting counters in a `table`

I wrote this plugin to aid the development of my own ESLint config settings and found it incredibly useful for keeping track of everything. I hope you find this module useful and please do let me know if you have any ideas on how to improve it.

Start with the issue description and the linked eslint-index documentation on npm to understand the proposed utility and its possible use with eslint-config-airbnb-base and eslint-config-airbnb. The issue does not identify repository files, tests, or a concrete change, so the intended scope and definition of done require clarification.

Written by the indexing model from the issue text.