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.

2018/burton1/README.md

@@ -22,7 +22,7 @@ make
 ./prog < prog.c
 ```
 
-### Alternate code:
+## Alternate code:
 
 An alternate version of this entry, [prog.alt.c](prog.alt.c), is provided
 This alternate code was supposed to compile without warnings, however

2018/ciura/README.md

@@ -21,7 +21,7 @@ make
 ./prog < README.md
 ```
 
-### Alternate code:
+## Alternate code:
 
 An alternate version of this entry, `prog.alt.c`, is provided.  As mentioned in
 the Author's remarks, the alternate version lacks a useful bug fix.

2018/ferguson/README.md

@@ -28,7 +28,7 @@ make
 make test
 ```
 
-### Alternate code:
+## Alternate code:
 
 The author provided an alternate version which has a simpler keyboard for the
 monkey Eric. See his comments under the 'keyboards' section, briefly referred to