Added "Interpreting LISP"

free-programming-books.md

@@ -966,6 +966,7 @@ See also [TeX](#tex)
 * [Common Lisp the Language, 2nd Edition](http://www.cs.cmu.edu/Groups/AI/html/cltl/mirrors.html)
 * [Common Lisp: A Gentle Introduction to Symbolic Computation](http://www.cs.cmu.edu/~dst/LispBook/) - David S. Touretzky
 * [Google's Common Lisp Style Guide](http://google-styleguide.googlecode.com/svn/trunk/lispguide.xml)
+* [Interpreting LISP](http://www.civilized.com/files/lispbook.pdf) - Gary D. Knott
 * [Let Over Lambda - 50 Years of Lisp](http://letoverlambda.com/index.cl/toc)
 * [Lisp Hackers: Interviews with 100x More Productive Programmers](https://leanpub.com/lisphackers) - Vsevolod Dyomkin
 * [Lisp Koans](https://github.com/google/lisp-koans)