cleanup winner README.md files

Fixed cases where there was a bad trailing backslash.

Improved a few cases where a code block was needed
to highlight some text.

Changed a few cases where a code block needed to
declared as, say, a sh code block.

Fixed a few cases where the winner information was not properly formatted.

Plus a few nits and clarifying text was added.

1990/dg/README.md

@@ -65,7 +65,7 @@ As for the rot13 algorithm, it relies on `index(3)` to find if the
 character is in the set `A-Za-z`. `l[]` is an array that gets filled
 with:
 
-```
+```c
 "nopqrstuvwxyzzzzabcdefghijklmmmmNOPQRSTUVWXYZZZZABCDEFGHIJKLMMMM"
 ```