I watched a video of CS50's Introduction to Game Development
https://online-learning.harvard.edu/course/cs50s-introduction-game-development
and decided to implement a similar Pong game while taking the opportunity
to learn Common Lisp along the way.

So, S-Pong is an implementation of the CS50 Pong, with some variations
of mine, in Common Lisp.

Tested with: SBCL.

To use: Put the spong directory in the local-projects repository of
quicklisp, and type:
(ql:quickload :spong)
(in-package #:com.the-blackbeard.spong)
(spong)

Have fun!