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.

2019/ciura/README.md

@@ -34,7 +34,7 @@ make
 ```
 
 
-### Alternate code:
+## Alternate code:
 
 There is an alternate version of this code that flushes stdout after writing a newline.
 See the Author's remarks for more information.

2019/duble/README.md

@@ -61,7 +61,7 @@ find . -name '.[A-Z]*' -delete
 
 though one might want to check that the program is not currently running. :-)
 
-### Alternate code:
+## Alternate code:
 
 An alternate version of this entry, [prog.alt.c](prog.alt.c), is provided.  This alternate
 code might not work as well on macOS.