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.

2015/endoh3/README.md

@@ -87,7 +87,7 @@ hijack the `main()` function call.  And then it interprets `main()` as an
 instruction sequence.
 
 It supports the minimal subset of instructions and addressing modes which are
-needed for [mullender.c](mullender.c) to work:
+needed for [mullender.c](%%REPO_URL%%/2015/endoh3/mullender.c) to work:
 
 * Instructions
   * BR: branch

2015/endoh3/index.html

@@ -427,7 +427,7 @@ Read it upside down.)</p>
 hijack the <code>main()</code> function call. And then it interprets <code>main()</code> as an
 instruction sequence.</p>
 <p>It supports the minimal subset of instructions and addressing modes which are
-needed for <a href="mullender.c">mullender.c</a> to work:</p>
+needed for <a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2015/endoh3/mullender.c">mullender.c</a> to work:</p>
 <ul>
 <li>Instructions
 <ul>