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/endoh2/README.md

@@ -29,11 +29,11 @@ What happens if you do
 
 ## Judges' remarks:
 
-Clever use of the C99 complex data type. The [spoiler](spoiler/) directory
+Clever use of the C99 complex data type. The [spoiler](%%REPO_URL%%/2020/endoh2/spoiler/spoiler.html) directory
 contains clues as to how some winning authors create / edit programs into ASCII
 shapes.
 
-With the source from the [spoiler](spoiler/) directory could you make the code
+With the source from the [spoiler](%%REPO_URL%%/2020/endoh2/spoiler/spoiler.html) directory could you make the code
 render for a larger terminal window?  How about adding more glyphs?