fix links in entry HTML files other than index.html

Fixed internal links in entry HTML files other than index.html.

Removed links to markdown files that otherwise used to
generate HTML files other than index.html.

Ran `make gen_other_html` to perform the above.

2004/gavin/gavin.html

@@ -138,7 +138,7 @@
 <ol type="1">
 <li><p>First, build the kernel and filesystem (just <code>make</code>). In short, you need to
 build this on an x86 Linux machine. If you wish to try to compile on an OS
-other than Linux you may need modify the <a href="Makefile">Makefile</a> to compile <code>sh</code>
+other than Linux you may need modify the <a href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2004/gavin/Makefile">Makefile</a> to compile <code>sh</code>
 using a cross-compiler that produces ELF binaries - i.e. a cross-compiler
 targeting x86 Linux. In short, you need to build this on an x86 Linux machine.</p></li>
 <li><p>Next, find a suitable machine to run the OS on. It should be perfectly safe,

2004/gavin/gavin.md

@@ -2,7 +2,7 @@
 
 1. First, build the kernel and filesystem (just `make`).  In short, you need to
 build this on an x86 Linux machine.  If you wish to try to compile on an OS
-other than Linux you may need modify the [Makefile](Makefile) to compile `sh`
+other than Linux you may need modify the [Makefile](%%REPO_URL%%/2004/gavin/Makefile) to compile `sh`
 using a cross-compiler that produces ELF binaries - i.e. a cross-compiler
 targeting x86 Linux.  In short, you need to build this on an x86 Linux machine.