Add ASDF files to Common Lisp

ASDF is a build system for common lisp. The .asd extension is just convention, as far as I can tell. The file is plain CL.

http://www.cliki.net/asdf

Some examples:

- https://github.com/edicl/hunchentoot/blob/master/hunchentoot.asd
- https://github.com/cmoore/inez/blob/master/inez.asd