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.

2013/birken/index.html

@@ -600,7 +600,7 @@ represented using ANSI escape sequences.</p>
 rate in which the terminal application receives and displays the <a href="https://en.wikipedia.org/wiki/ANSI_escape_code">ANSI
 escape</a> sequences.</p>
 <p>To slow down the output programmatically, introduce a delay immediately after the
-call to <code>fflush(3)</code> (N.B: see <a href="birken.alt.c">birken.alt.c</a>).</p>
+call to <code>fflush(3)</code> (N.B: see <a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2013/birken/birken.alt.c">birken.alt.c</a>).</p>
 <h3 id="ioccc-size-tool-bug">IOCCC Size Tool Bug</h3>
 <p>This program demonstrates how to exploit a bug in IOCCC size tool version
 <code>2013-07-30-v17</code>. The first line of the program is reproduced below.</p>