provide a much better url for "Open Data Structures" (#2310)

* provide a much better url

with python, java, c++ versions; slovenian and turkish translations and source code

* remove trailing slash

free-programming-books.md

@@ -279,7 +279,7 @@
 * [Linked List Basics](http://cslibrary.stanford.edu/103/LinkedListBasics.pdf) (PDF)
 * [Linked List Problems](http://cslibrary.stanford.edu/105/LinkedListProblems.pdf) (PDF)
 * [Matters Computational: Ideas, Algorithms, Source Code](http://www.jjj.de/fxt/fxtbook.pdf) (PDF)
-* [Open Data Structures: An Introduction](http://www.aupress.ca/index.php/books/120226) - Pat Morin
+* [Open Data Structures: An Introduction](http://opendatastructures.org) - Pat Morin 
 * [Planning Algorithms](http://planning.cs.uiuc.edu)
 * [Problems on Algorithms (Second Edition)](https://larc.unt.edu/ian/books/free/license.html) - Ian Parberry (use form at bottom of license)
 * [Purely Functional Data Structures](http://www.cs.cmu.edu/~rwh/theses/okasaki.pdf) (PDF)