Changing heading level of 'Alternate code'

Change level 3 (###) to level 2 (##):

    sgit -e 's/^### \(Alternate code\)/## \1/g' '*README.md'

which is the same as:

    sgit -e 's/^### Alternate code/## Alternate code/g' '*README.md'

This is per discussion in GitHub.

2004/gavare/README.md

@@ -22,7 +22,7 @@ make
 ./gavare > ioccc_ray.ppm
 ```
 
-### Alternate code:
+## Alternate code:
 
 The author provided [on their web page for the
 entry](https://gavare.se/ioccc/ioccc_gavare.c.html) an unobfuscated version that was used