Added songho.ca

Added Realm of Racket book and fixed formatting issue between textbook and next header

Add new version of php book

added course names to Berkeley free courses

Add two books: The Art of Community and The Open Source Way

Added discover flask from Real Python to web development courses list.

quelques introductions à lua

Added book about statistics in czech language

Updated the broken link for "Mathematics for computer science" with the available one

that contains nice OpenGL learning materials.

fix Lisp/PCL link (404 error)

I changed the name by the book title , so it makes more sense !
the reference of the license into file 
http://www.etelg.com.br/paginaete/downloads/informatica/php.pdf

adding a new reference to php
the reference of the license is here! https://github.com/PHPSP/php-the-right-way

adding a new reference to php

Atualizando fonte do PHP para uma atual e renomada, a antiga era de 2000, quando o PHP era praticamente outra linguagem.

Add a ukrainian translation of the http://learnyouahaskell.com

Add "Practical Common Lisp" book

Alphabetizing of the "bg" section

Alphabetized the Bulgarian file.

Alphabetized free-courses-en.md

Add FR resource - Arduino

Update free-programming-books-ko.md

Update free-programming-books-it.md

Added [Try MongoDB] to Interactive Tutorials

Update free-programming-books.md