Tests docs check script

[pnevyk]

This PR adds a script that checks if there are tests and docs for each rule and they are included in their corresponding "index" files. It was discussed in #366. What exactly is checked is documented in the header of the script. I added this check to pre-commit hook.

Thanks to this script I discovered that three rules have no assertions in readme and that for one rule tests were not executed. I fixed these issues.

Side note: The new post-commit hook crashes when the current branch is not in .git/config yet, which I think is before the push to a remote server. This crash comes from gitdown and transitively from gitinfo. Also in contributing guide there is a sentence that the documentation is built using CI but it seems that it is not true anymore (imo it was removed in this commit). I think that generating docs in CI is better approach than in post commit hook but that's just my hint.

[gajus]

Looks great. Thank you.

Is it ready to be merged?

[pnevyk]

If you like it then I think that yes. Maybe the script can be added to travis script but that's up to you. And if you can in some time resolve the side note I wrote in the description of this PR, it would be great.

[gajus]

🎉 This PR is included in version 3.1.2 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot 📦🚀

[gajus]

Side note: The new post-commit hook crashes when the current branch is not in .git/config yet, which I think is before the push to a remote server. This crash comes from gitdown and transitively from gitinfo.

This is a known issue gajus/gitinfo#17

Also in contributing guide there is a sentence that the documentation is built using CI but it seems that it is not true anymore (imo it was removed in this commit). I think that generating docs in CI is better approach than in post commit hook but that's just my hint.

The same issue is preventing generating docs in Travis.

https://travis-ci.org/gajus/eslint-plugin-flowtype/jobs/447405101