Add alt code to 2004/gavare

On the author's web page for the entry
(https://gavare.se/ioccc/ioccc_gavare.c.html) they provided an
unobfuscated version of the code. The code has been added to the repo
and Makefile as well.

To compile use:

     make alt

and use gavare.r3 as you would use gavare.

2004/gavare/.gitignore

@@ -1,2 +1,3 @@
 gavare
 ioccc_ray.ppm
+gavare.r3