* fixed link

* remove trailing slash to satisfy linter

* Added Microservice Databases: Migrating from Relational Monolith to Distributed Data (By O'Reilly)

* fixed concerns

* Added the bash book to the books section

I have attempted to add the bash book to the book section again. There was  an issue the last time , i tried to propose the file change as i had not placed it in alphabetical order. Someone please review this :)

* fixed alphabetization

* Add couple of book for PHPUnit

* Added PDF text to the links

* Added PHPUnit Best Practices

* Alphabetically arranged

* [JavaScript and Node FUNdamentals](https://web.archive.org/web/20150327025334/https://leanpub.com/jsfun/read) - Azat Mardanov is not a free programming book

* implement #2357

* misc cleanup

Author deleted page partially.
He write message on the page: This book has been removed as it will shortly be published by APress.

*  added link to Directory of free Javascript ebooks

* link fix Directory of free Javascript ebooks and sorting in alphabetical order

* updated link

*  Sorry, Corrigir e retirei o link

* Revert "correcting and removing the link

This reverts commit 5059e43931299d7fcdd017ae53c8c742ea36dd1f.

* 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

* 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.

* 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)

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

* 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.

* 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

* 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

* 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/

* Updates free-programming-books.md

Adds a link to a free image optimization book

* fixes failing build

removed trailing slash

* adds author name

I'm sure @tpetricek can confirm his book is not free

the Lua Programming Gems book is not freely available (apart from the second chapter and notes for some other chapters), and is not a general guide to the language; the first edition of Programming in Lua, however, *is* freely available, and *is* a guide for learning the language in general.

* Added a new Scala book

"Functional programming for mortals" is a very good book about Scala and it is free to read on the web.

* Removed the '*' at the end

* Added Thinking in HTML book (free eBook) to HTML section

* Update free-programming-books.md

* Update free-programming-books.md

* Added "Julia language: a concise tutorial"

https://www.gitbook.com/book/sylvaticus/julia-language-a-concise-tutorial

* Removed PDF tag and added the second blank line

* This book doesn't seem to have anything to do with Mathematica.

* Added a free/open book on Algorithms in Python

Linked to the github repo, but it links to a PDF download from there.

* added author name

* Added CodeIgniter Framework

* Added CodeIgniter Framework

* Update free-programming-books-ru.md

* Update free-programming-books.md

* Update free-programming-books.md