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.

1988/isaak/README.md

@@ -19,7 +19,7 @@ code](#alternate-code) below.
 ./isaak
 ```
 
-### Alternate code:
+## Alternate code:
 
 The original version of this code is in [isaak.alt.c](isaak.alt.c).
 The original entry starts with the line: