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/dds/README.md

@@ -24,7 +24,7 @@ make all
 
 Give the following lines as input:
 
-```
+```basic
 OLD LANDER.BAS
 RUN
 ```

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"
 ```
 

1990/tbr/README.md

@@ -23,7 +23,7 @@ output due to a warning at runtime that was interspersed with the output of the
 program. For instance it would show:
 
 ```sh
-$ ./tbr
+./tbr
 $ warning: this program uses gets(), which is unsafe.
 ```
 
@@ -39,7 +39,7 @@ below, in the [alternate version](#alternate-code) section.
 
 ```sh
 ./tbr
-# enter some shell commands
+$ enter some shell commands
 ```
 
 NOTE: globs do not work with this entry. Why?
@@ -53,11 +53,14 @@ just `exit` or `logout`? Hint: see the authors' remarks.
 
 ```sh
 ./tbr
-ls -l tbr tbr.c
+$ ls -l tbr tbr.c
+
 # notice how the following does not work:
 ls tbr*
+
 # try figuring out how this entry works in an editor:
 vi tbr.c
+
 # then figure out how to exit vi :-)
 ```