Add Math Books from aimath.org (#5256)

* Add Math Books from aimath.org

* Fix Trailing Slashes

* Fix Alphabetical Order?

* Fix Alphabetical Order

* Fixed language and categories

* Fixed language and categories for -ko.md

* Removed most PDF links from addition.

* Replace German Resource with Direct Link to PDF

books/free-programming-books-fr.md

@@ -27,6 +27,7 @@
   * [TeX](#tex)
 * [Lisp](#lisp)
 * [Lua](#lua)
+* [Mathématiques](#math%C3%A9matiques)
 * [Meteor](#meteor)
 * [Perl](#perl)
 * [PHP](#php)
@@ -196,6 +197,11 @@
 * [Traité de programmation en Common Lisp](http://dept-info.labri.fr/~strandh/Teaching/Programmation-Symbolique/Common/Book/HTML/programmation.html) - Robert Strandh et Irène Durand
 
 
+### Mathématiques
+
+* [Calcul mathématique avec Sage](http://sagebook.gforge.inria.fr) - Paul Zimmermann et al.
+
+
 ### Lua
 
 * [Introduction à la programmation Lua](http://www.luteus.biz/Download/LoriotPro_Doc/LUA/LUA_Training_FR/Introduction_Programmation.html)