Add missing ':' to Alternate code sections

This was done as:

    sgit -e 's/\(# Alternate code\)$/\1:/g' '*README.md'

The heading levels and other things to do with alternate code that are
being discussed have not been addressed here. That will come later. This
is, as noted, just adding the missing ':' where it was missing.

The command does NOT touch it when it is not prefixed with '# ' because
there are cases where normal lines end with 'Alternate code' (these will
be turned into links later on).

2004/arachnid/README.md

@@ -36,7 +36,7 @@ QWERTY keyboards.  Rogue players, vi users, and Dvorak typists are
 invited to get lost (or use the alt version)!
 
 
-### Alternate code
+### Alternate code:
 
 To use:
 

2004/hoyle/README.md

@@ -24,7 +24,7 @@ make
 ./hoyle 2 0 1 0 -0.001
 ```
 
-### Alternate code
+### Alternate code:
 
 An alternate version of this entry, [hoyle.alt.c](hoyle.alt.c), is provided.
 This alternate code has a missing newline and used a non-standard tab stop size.

2004/kopczynski/README.md

@@ -42,7 +42,7 @@ What happens if you feed the program source to the program? Can you figure out
 why?
 
 
-### Alternate code
+### Alternate code:
 
 The judges modified the program to print its result.  The original
 program returned the result as an exit code: