Fixed link to How to be a Programmer
Merge pull request #463 from sugarjig/patch-1

Fixed link to How to be a Programmer
Update free-programming-books-pl.md
Merge pull request #464 from zawieja/master

Update for 'pl' file : Book added: Pisanie OS
Update free-programming-books.md

added "Deep C" under entry of C material.
Update free-programming-books.md

changed "Graphics User Interfaces" into "Graphical User Interfaces"
Merge pull request #465 from swchoi727/master

Update free-programming-books.md
Fix a link
Update free-programming-books.md

Added the JS Robots chapter from Expert Javascript book
Merge pull request #466 from tk120404/patch-2

Update free-programming-books.md
Add "CoolAid: The Cool 2013 Reference Manual"

Describes the programming language Cool: the Classroom
Object-Oriented Language.
Merge pull request #467 from tcort/cool

Add "CoolAid: The Cool 2013 Reference Manual"
added free programming books in Turkish
free programming books in Turkish
Merge pull request #468 from erdemoncel/master

Free programming books in Turkish