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.

2015/howe/README.md

@@ -44,7 +44,7 @@ cp war-and-peace.txt nuked.tmp
 ./avgtime.sh 100 ./prog war-and-peace.txt nuked.tmp
 ```
 
-### Alternate code:
+## Alternate code:
 
 An alternate version of this entry, `prog.alt.c`, is provided.
 This alternate code does not use a 64 bit FNV hash.