Format fix 1980s and 1990s README.md files

I also updated the todo.md file as I left some things out that have to
be done. I only explicitly named one thing but when I go over them as a
final pass I will address the things in question (some will require
discussion).

1990/README.md

@@ -1,28 +1,27 @@
-1990 marked the "The Seventh International Obfuscated C Code Contest"
+# 1990 marked the "The Seventh International Obfuscated C Code Contest"
 
-
-Look at the README.md file for the given winner for information
-on how to compile the winner and how to run the winning program.
+Look at the README.md file for the given winning entry for information
+on how to compile it and how to run the winning program.
 Look at the winning source and try to figure how it does what it does!
 You may then wish to look at the Author's remarks for even more details.
 
 This year, the Grand Prize won a standing ovation at USENIX.
 
-The "Strangest abuse of the rules" award was given this year to stress
-the fact that starting in 1991, entries should be shell-specific.
+The ["Strangest abuse of the rules"](1990/stig/README.md) award was given this
+year to stress the fact that starting in 1991, entries should be shell-specific.
 
 This year was the first year that we accepted ANSI C entries.  It was
-interesting to note that the ANSI C entries were as a whole less
-portable than the K&R C entries.  We hope that in future contests
-people will enter more obfuscated and challenging ANSI C programs.
+interesting to note that the ANSI C entries were as a whole less portable than
+the K&R C entries.  We hope that in future contests people will enter more
+obfuscated and challenging ANSI C programs.
 
 We would like to thank Barbara Frezza (loving wife of Larry Bassel) for
 her role as official chef of the contest.  Her opinions regarding
 some of the contest entries were appreciated.
 
-Rules and results were posted to comp.lang.c, comp.sources.unix, and
-alt.sources.  They have been made available on a wide number of Usenet
-archive sites such as uunet.
+[Rules](rules.txt) and [results](https://www.ioccc.org/years.html#1990) were
+posted to comp.lang.c, comp.sources.unix, and alt.sources.  They have been made
+available on a wide number of USENET archive sites such as uunet.
 
 =-=