Remove 'America' (A) from 'USA' :-)

This to make the country code consistent with mkiocccentry (and I guess
international standard country codes).

This affects many README.md files and (for one line) winners.csv.

1996/README.md

@@ -72,7 +72,7 @@ contest have not been formed at this time and are not expected to be
 ready for distribution until late February 1998.
 
 So what happened to 1997?  Well the next USENIX Technical Conference
-will be held Jun 15-19, 1998 (in New Orleans, USA).  The 18 month
+will be held Jun 15-19, 1998 (in New Orleans, US).  The 18 month
 span between conferences will cause the IOCCC to skip over 1997.
 
 Be sure to wait until the 1998 rules are posted before submitting entries.

1996/dalbec/README.md

@@ -3,7 +3,7 @@
 John Dalbec  
 20 Squire's Ct.	(home address)  
 Canfield, OH 44406  
-USA  
+US  
 <https://jpdalbec.people.ysu.edu>
 
 ## To build:

1996/huffman/README.md

@@ -4,7 +4,7 @@ Ken Huffman
 Applied Innovation Inc  
 5800 Innovation Dr.  
 Dublin, OH 43016  
-USA  
+US  
 <http://www.huffmancoding.com>  
 huffmancoding@gmail.com  
 

1996/rcm/README.md

@@ -3,7 +3,7 @@
 Ron McFarland  
 7941 Fawncreek Drive  
 Cincinnati, Ohio 45249  
-USA  
+US  
 
 ## To build:
 

1996/westley/README.md

@@ -3,7 +3,7 @@
 Brian Westley (Merlyn LeRoy on Usenet)  
 1906 James Ave.  
 St. Paul, MN  55105  
-USA  
+US  
 <http://www.westley.org>  
 
 ## To build: