fix: add rule documentation

[macklinu]

Resolves #61

First step of this PR was converting each rule to export an object instead of a function using eslint-transforms, specifically the new-format-rule transform. I ran the following command.

$ npx eslint-transforms new-rule-format rules/*.js

I edited a few rules manually to add the meta.docs.url object, but after that I installed eslint-plugin-eslint-plugin and enabled the require-meta-docs-url rule in the rules/ directory. By running npm run lint -- --fix from the root of the repo, all rules now have a valid meta.docs.url that points to the proper documentation section of the README.

The Travis script has been updated to run this lint command. Now that this repo has Standard and ESLint installed, there are two tools that lint the codebase. I'm wondering if down the line we use a tool like Prettier for code formatting and then rely solely on ESLint for linting the codebase. 🤔 (That's for another issue/PR.)

[Arcanemagus]

Now that this repo has Standard and ESLint installed

Note that this is the same as saying you have ESLint installed twice, since Standard is just a wrapper around ESLint with a predefined config 😉. You can base your ESLint configuration on eslint-config-standard to get the same effect.