* Add `Front-End Developer Handbook 2016`

* Add `Front-End Developer Handbook 2017`

* Add `Front-End Developer Handbook 2018`

* Add `Front-End Developer Handbook 2019`

Resolves #6931

* Written by Cody Lindley

* Add `JavaScript (ES2015+) Enlightenment`

* lint: alphabetize-lists

* format: Complete authoring of `React Enlightenment`

* only one link is enough, it said the boss

* delete `sponsored by` author: `Frontend Masters`