move fix thanks a file, update top level html links, rename CONTRIBUTING.md

The fix thank you's have been moved from `README.md` to
`thanks-for-fixes.md`.

**WARNING**: Some mistakes may have been made in doing this.
We presume later changes by others will correct any issues.

The `CONTRIBUTING.md` was renamed `how-to-enter.md`.

A 3rd line of links was added to top level html such as
`contact.html`, `index.html`, `judges.html`, `winners.html`,
and `years.html`.

Improved blank line use in a number (but not all) `README.md` files.

bugs.md

@@ -1,4 +1,4 @@
-# BUGS and (MIS)FEATURES
+# Bugs and (Mis)features
 
 There are a number of known problems with IOCCC winners: many of
 which have to do with differences between today's compiler environments