* Added 苦しんで覚えるＣ言語 in ree-programming-books-ja.

* Sort in dictionary order

Written by Massimiliano Tarquini and Alessandro Ligi

* remove defunct links

* Update free-programming-books.md

Adding Node.js book reference

* Update free-programming-playgrounds.md

Added codesandbox.io under React (and removed the react reference from its listing on JavaScript).
Added a Java section and linked to repl.it
repl.it actually has sandboxes for most of the languages listed here, and maybe some others, but I didn't add them all in. The Swing support for Java is new, and has some bugs. They didn't respond to my report, so I think they are spread a little thin.

* add spaces to satisfy linter

* add space to satisfy linter
Co-authored-by: NEric Hellman <eric@hellman.net>

The textbook written for the course on python is freely licensed ([CC-BY-NC-ND](https://creativecommons.org/licenses/by-nc-nd/4.0/)), so it seems worth being added.

* Misc category cleanup

* Fix

* Removed the CS For All book

It's just a set of problems and the textbook is no longer available for free online.

This course now has restricted access. HTTP Response: Request failed with status code 403.

Page not found for link http://tableless.com.br/o-que-nodejs-primeiros-passos-com-node-js

* New books from the Syncfusion's Succinctly series

* Fix

* More books

* Cleanup

* Fixes

* One more fix

* O'Reilly cleanup

* Added the missing PDF annotation

* New MIT Open Access books

* Alphabetic fix

* Danish programming books added

* Danish link to README

* Update a Java book URL - #2990

Changes:
- The book 'Object-Oriented vs. Functional Programming' has a .csp link
- Also a sign-up is required to read the book since it's hosted at oreilly.com
- The contributing guide is against a hosting service and required sign-up.
- That is why this PR is created.

* remove ? link
Co-authored-by: NEric Hellman <eric@hellman.net>

* added spring data reference

* satisfy linter
Co-authored-by: NEric Hellman <eric@hellman.net>

- Fixed a couple of links to topics in the page
- Removed a course that is accessible only to students of the university which made the course
- Added three courses

Some of our Udacity listings added '(Udacity)' as and access note. This PR makes the practice uniform. We can consider other platforms case by case. In general, I feel that when the platform offers additional services that make it matter what platform a course is on, the addition of an access note is useful.

Comments welcome on appropriateness of  the access notes.