* Clean up the Oberon books

The Project Oberon book was duplicated under both Operating Systems and
Misc; plus a better link for Programming in Oberon.

* Add direct PDF links and authors for Oberon books

Add R section to playground and add R-Fiddle to it.

* add "Python-Kurs"

* correction: move to courses

* add empty lines to satisfy linter

* Added a few swedish developer podcasts

* Changed link protocol to https where applicable and added trailing new

* Added a link in the README to the Swedish podcasts file

* Update free-programming-books.md

Added Django Girls tutorial. Since it's not an interactive tutorial i have added it to books section.

* Update free-programming-books.md

Moved Django Girls Tutorial to the top of the Django books list according to alphabetic order.

* Add Procedural Content Generation in Games

* Remove trailing slash

Remove trailing slash to fix a CI-flagged error.

* Added a course in Web Development

Added Freecodecamp in web development. Free code camp is a free course featuring building projects and getting certificates.

* update free code camp in alphabetical order

* update verilog

update a free source of verilog quick reference

* substituted authoritative source for the quick reference guide

(PR has been sitting for a year)

* add "Framework Backbone (Javascript)"

- Série de artigos (tutoriais) sobre o framework Backbone para JavaScript
- http://www.devfuria.com.br/
- pt-br

* satisfy linter!

added Funtional C ; free download & more info at https://research.utwente.nl/en/publications/functional-c (#2613)

Fix a small mistake that causes errors in display of the courses list.

Delete Book which not free now

* Replace homepage with GitHub repository link

problem-sets-competitive-programming.md: Replace homepage
link of problembook with github repository link which contains
downloadable pdf links.

* Remove broken links

Remove broken links and update available links from
web.archive.org.

* Update broken link with updated link.

Update the description for the updated link.

* Update broken links with links from web.archive.org

Remove dead links.

* Restore path to original link instead of web.archive.org

The link seems to be working fine. It was not loading
on my network, probably due to regional restrictions.

* Remove github link which is no longer maintained.

Github link consisted of list of Big Data resources.
The repository has been deleted by the user.
Hence deleting the entry.

* added Ray Wenderlich Free tutorial in iOS section

* just a spelling change

* add back space to satisfy linter

* Add Clojure by Example

It's an example-based alternative to reading a long, in-depth book.

* Fix alphabetic order from last commit

Clojure section addition in wrong position.

* Add author to clojure by example

Minor Markdown fixes.

* Adicionado uma nova apostila de Git

* add PDF notation

* Update Gambas links

Updated broken Gambas beginner's guide link, and add additional link to Gambas resources since the original book's website has been taken down

* removed gambas links

Not sure the book is free anymore, and realised second link doesn't comply with contribution guidelines as it's not an actual book

* Re-add beginner's guide to gambas

* Update Verilog courses

Renamed `SystemVerilog` section to `Verilog / VHDL / SystemVerilog` because they are 3 different hardware description languages. Grouped them together so that all the Verilog resources can be found in one spot. Added new course as suggested in #2151

* Reorder Verilog courses by alphabetical order

* Add new course suggested by @mramdas

* Reorder Verilog courses

* Fix style

* Remove duplicate

* Remove broken link

* Change broken link

* Added Bootstrap

* Update free-programming-books-ua.md

* Update free-programming-books-ua.md

* R: Add Introduction to Statistical Learning by Hastie et al

* R: sort alphabetically

* add hack language

closes #2097

* Whoops! Wrong list.

* aaaaarg

* add notations for bookboon

* satisfy linter

Unofficial PDF version of "Category Theory for Programmers" by Bartosz Milewski, converted from his blogpost series. Blog content licensed as CC BY 4.0 International as seen at https://bartoszmilewski.com/about/

* fix grammar typo

* Fix Azerbaijani Docs Links

* reorder russian courses

and add link to readme

* О (cyrillic) not O

* Add Python courses

* Fix formatting

* Fix formatting