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.

2020/burton/README.md

@@ -37,7 +37,7 @@ arg. It might also print strange output with more than one arg.
 ./prog 128 128 128 128
 ```
 
-### Alternate code:
+## Alternate code:
 
 By default, this code compiles for Little Endian machines.
 An alternate version is also compiled for Big Endian machines.

2020/endoh1/README.md

@@ -29,7 +29,7 @@ make
 ./prog unwinnable.txt
 ```
 
-### Alternate code:
+## Alternate code:
 
 An alternate version of this entry, [prog.alt.c](prog.alt.c), is provided.  This
 alternate code lacks the additional rule to flag all unprobed cells.  See the

2020/endoh3/README.md

@@ -23,7 +23,7 @@ make
 # And watch closely for 15-20 seconds
 ```
 
-### Alternate code:
+## Alternate code:
 
 An alternate version of this entry, `prog.alt.c`, is provided.  This alternate code uses Unicode letters.
 

2020/kurdyukov1/README.md

@@ -25,7 +25,7 @@ echo IOCCC | ./prog
 ./prog < prog.x86_64.asm
 ```
 
-### Alternate code:
+## Alternate code:
 
 An even smaller alternate version of this entry, prog.alt.c, is provided.  This code does not contain any headers, nor any workaround for WIN32 based platforms.
 

2020/kurdyukov3/README.md

@@ -28,7 +28,7 @@ echo International Obfuscated C Code Contest | ./prog
 ./prog < input.txt
 ```
 
-### Alternate code:
+## Alternate code:
 
 There is an alternate version of this code in `prog.alt.c` where the main code is a macro.