Added elements of programming to C++ list (#3431)

* Added elements of programming to C++ list

* Fix the alphabetical order of Elements of Programming on C++ list

* Removing a trailing slash from Elements of Programming URI

free-programming-books.md

@@ -985,6 +985,7 @@ Kerridge (PDF) (email address *requested*, not required)
 * [C++ Today](http://www.oreilly.com/programming/free/c++-today.csp) (email address *requested*, not required)
 * [C++ Tricks](http://www.bordoon.com/cplusplus/book_wrapper.html)
 * [CS106X Programming Abstractions in C++](http://web.stanford.edu/class/cs106x/)
+* [Elements of Programming](http://elementsofprogramming.com) - Alexander Stepanov and Paul McJones - (PDF)
 * [Financial Numerical Recipes in C++](http://finance.bi.no/~bernt/gcc_prog/recipes/) - Bernt Arne Ødegaard
 * [Game Programming Patterns](http://gameprogrammingpatterns.com)
 * [Google's C++ Style Guide](https://google.github.io/styleguide/cppguide.html)