* Update free-programming-playgrounds.md

Added a few C++ playgrounds to the list

* Update free-programming-playgrounds.md

Placed the links in alphabetical order. I mistakenly didn't do this in my initial PR.

* chore: improve angular / angular.js listings

- Wellnaming section
- fix book title, add format, add creators as is seen in file

via EbookFoundation/free-programming-books#4940

* chore: improve angular / angular.js listings

- Wellnaming section
- fix book title, add format, add creators as is seen in file

via EbookFoundation#4940

* chore: improve angular / angular.js listings

- Wellnaming sections (typescript>angular, javascript>angularjs)
- Add free resources to complete listing with at least 2 items, mainly from html.it website.
- fix titles, add format, add creators as is seen in linked files

via EbookFoundation/free-programming-books#4940

* chore: improve angular / angular.js listings

- Move Angular resources from Angular.js to TypeScript
- Add more resources to avoid single sections

via EbookFoundation/free-programming-books#4940

* chore: improve angular / angular.js listings

- Sections (typescript>angular, javascript>angularjs)
- Add free resources to complete listing with at least 2 items.
- fix titles, add format, add creators as is seen in linked files

via EbookFoundation/free-programming-books#4940

* chore: improve angular / angular.js listings

- Move Angular resources to TypeScript
- Well-naming sections
- fix book title, add format, add creators as is seen in files

via EbookFoundation/free-programming-books#4940

* chore: improve angular / angular.js listings

- Move Angular resources from Angular.js to TypeScript
- Add more resources to avoid single sections
- Complete notes, titles, format, authors

via EbookFoundation/free-programming-books#4940

* chore: improve angular / angular.js listings

- Well-naming section
- Complete notes, titles, format, authors

via EbookFoundation/free-programming-books#4940

* chore: improve angular / angular.js listings

- Handle both as anchor. angular and angular.js

via EbookFoundation/free-programming-books#4940

* chore: improve angular / angular.js listings

- Add http://plnkr.co as valid playground for both
- Add https://stackblitz.com as valid playground for both

via EbookFoundation/free-programming-books#4940

* chore: Angular.js > AngularJS and other pitfails

- Use AngularJS as title/name
- Fix some errors with heading levels in Javascript/Typescript section
- Finish to move some resources accoding their content

via EbookFoundation/free-programming-books#4940

* feature: sections crosslinks as blockquotes

* feature: sections crosslinks as blockquotes

Mainly for AngularJS/Angular, Javascript/Typescript,
web, databases listing sections

* chore: revert scoping crosslinks only to Angular

* Update SoloLearn playground links

- Update SoloLearn playground links: Web, Node.js, Java, Python, Ruby
- Add missing language support: C, C++, C#, Go, Kotlin, PHP, R, Swift

* Fix CI/CD linting errors

* reorganize files

1. make it easier to find files
2. reduce scrolling to get to README on main view of repo

* remove tr.txt again

Added extendsclass, an online PHP playground

* ClojureScript addition

Added a new ClojureScript online playground

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

* Added Blockchain Programming Book

* Added the packt link

* Added a Kotlin Playground

* The Kotlin Playground

* Added a Flutter Playground

* Removed the Leadin Slash

* Added Ruby Playground

* Added a new line at the end of free programming playgrounds

* Fixed the spacing in free-programming-books-fa_IR.md

* Fixed More errors in the above file

* Errors fixed in free-programming-books-fa_IR.md

* Some more changes

* Restored the previous farsi file

* Added an Elm Playground

* Update free-programming-playgrounds.md

* Update free-programming-playgrounds.md

* Added Blockchain Programming Book

* Added the packt link

* Added a Kotlin Playground

* The Kotlin Playground

* Added a Flutter Playground

* Removed the Leadin Slash

* Added Ruby Playground

* Added a new line at the end of free programming playgrounds

* Fixed the spacing in free-programming-books-fa_IR.md

* Fixed More errors in the above file

* Errors fixed in free-programming-books-fa_IR.md

* Some more changes

* Restored the previous farsi file

* Added Kaggle Python course

* Add Python Runestone to interactive tutorials

* added author

* Added Python and Java playground

* add space back

* lower cased name

* fixed capitalization for Java and JavaScript

* Added Rextester to R Interactive Playgrounds

* swapped order

* switched order

* Added Blockchain Programming Book

* Added the packt link

* Added a Kotlin Playground

* The Kotlin Playground

* Added a Flutter Playground

* Removed the Leadin Slash

* Added Kaggle Python course

* Add Python Runestone to interactive tutorials

* added author

* Added Python and Java playground

* add space back

* lower cased name

* fixed capitalization for Java and JavaScript

* Added Blockchain Programming Book

* Added the packt link

* Added a Kotlin Playground

* The Kotlin Playground

* Add esfiddle

* Make alphabetical

* Remove / at the end of url

* Added GDScript

* Update free-programming-playgrounds.md

* Add javatpoint android free tutorial

* add python playground

* Add interactive new Android tutorial section

javatpoint android tutorial

* del prev change

* change python playground title

* Add "What I Wish I Knew When Learning Haskell"

Follow up #3173.

* Update free-programming-books-zh.md

Follow up #3330.

* added competitive programming link

Follow up #3398.

* Added Redis interactive tutorial

* updated docs location

* Update free-programming-playgrounds.md

Added python interpreter

* Update free-programming-playgrounds.md

Fixed linter error

Added an interpreter for python

* Add Playground Reference Site for Dart & Flutter

* fix format

* Fix url dartpad.dev format

* Fix lint

* add: kubernetes and docker play grounds

* fix: sorting in alphabetical order

* fix: remove trailing slash

* Update kotlin playground

The current kotlin playground is obsolete.
Updated to the new playground link.

* remove '/' to satisfy linter

Always check the Travis-CI output!
Co-authored-by: NEric Hellman <eric@hellman.net>

* Move a playground link to CSS section

FlexBox is a CSS feature.
This move is consistent with other files.

* Fix index in english free-programming-playgrounds

* Move a section according to alphabetical order

* Remove offline link pyfiddle.io

Shutdown confirmed: https://github.com/priyankcommits/pyfiddleio/issues/7

* 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>

* Update free-programming-playgrounds.md

* Update free-programming-playgrounds.md

This reverts commit 48478fe1.

add sqlite fiddle in SQL

* Added OCaml playground

* delint

* added Solidity

* added Solidity

* added Solidity

* bitcoin book added

* fixed ordering on bitcoin book entry

* added authors for bitcoin and solidity books

* added Bitcoin and cryptocurrency Princeton book

* elm interactive playground added (ellie)

* free elm books added

* elm podcast added

* corrected spacing

* reordered elm books into existing category

* reordered format and author

* removed trailing /s

* fixed alphabetical ordering

* Fix playgrounds alphabetical order

* Add Scala to playgrounds index

* Add online Swift playground

* remove broken links

* remove broken links

* remove broken links

* fix broken links

* fix broken links

* fix broken links

* fix broken links

* remove broken links

* remove broken links

* remove broken links

* remove broken links

* remove broken links

* remove broken links

* remove broken links

* remove broken links

* remove broken links

* remove broken links

* replace dead link