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.

1995/cdua/README.md

@@ -33,7 +33,7 @@ solving the maze. This is a feature, not a bug. See [bugs.md](/bugs.md) for more
 details.
 
 
-### Alternate code:
+## Alternate code:
 
 This version uses `usleep(3)` with the `Z` (defined in the Makefile, default
 `3000`) microseconds to make it easier to see the maze being solved in real

1995/garry/README.md

@@ -28,7 +28,7 @@ make all
 ```
 
 
-### Alternate code:
+## Alternate code:
 
 While it may not have been the intention of the author, the
 judges noted that the C pre-processed version (with the `#include`s

1995/vanschnitz/README.md

@@ -26,7 +26,7 @@ make clobber all LEVEL=6
 ./vanschnitz
 ```
 
-### Alternate code:
+## Alternate code:
 
 The authors provided a spoiler version of the program. Originally uuencoded we
 have decoded it for the wider audience in [spoiler.c](spoiler.c). The