fix many internal links

Fixed a number of internal links that need to
go to the GitHub site.

Ran `make www` to perform the above.

2020/kurdyukov4/README.md

@@ -30,7 +30,7 @@ context length decreases:
 
 ## Judges' remarks:
 
-We were able to [write our own program](rand.c) performing the same trick using
+We were able to [write our own program](%%REPO_URL%%/2020/kurdyukov4/rand.c) performing the same trick using
 the (still non-standard, for some reason) library function `memmem()`, but that
 way it works too fast regardless of the context length, and it's much less fun.