Added a mathematics book. (#5328)

* Added a book.

* Changed the section for APL book.

books/free-programming-books.md

@@ -993,6 +993,7 @@ Kerridge (PDF) (email address *requested*, not required)
 
 * [A Practical Introduction to APL1 & APL2](http://robertson.uk.net) - Graeme Donald Robertson (PDF)
 * [A Practical Introduction to APL3 & APL4](http://robertson.uk.net) - Graeme Donald Robertson (PDF)
+* [Introduction to College Mathematics with A Programming Language (1978)](http://www.softwarepreservation.org/projects/apl/Books/CollegeMathematicswithAPL) - E. J. LeCuyer (PDF)
 * [Mastering Dyalog APL](http://www.dyalog.com/mastering-dyalog-apl.htm) (PDF)