improve entry index.html navbar links

We improve entry `index.html` navbar links by allowing the
next and previous to link across years.

The `make genpath` now forms `.allyear`, which is a
sorted contamination of all YYY level `.year` files.

Updated `make help` to reflect the  `make genpath` functionality.

Updated FAQ 6.8 to talk about the `.allyear` file.
Fixed links to `.top` and `.allyear' to refer to GitHub.

Changed `bin/subst.entry-navbar.awk` VERSION from "1.2 2024-03-02"
to "1.3 2024-08-02".

Changed `bin/subst.entry-index.sh` VERSION from "1.3.5 2024-08-05"
to "1.4 2024-08-09".

Performed `make www` to accomplish the above and to test under macOS.

2013/robison/index.html

@@ -373,19 +373,19 @@
 </div>
 
 <!-- END: this line ends content from: inc/header.default.html -->
-<!-- START: this line starts content from: inc/navbar.last.html -->
+<!-- START: this line starts content from: inc/navbar.mid.html -->
 
 <div class="navbar">
-  <a class="Left" href="../morgan2/index.html">&larr; morgan2</a>
+  <a class="Left" href="../morgan2/index.html">&larr; 2013/morgan2</a>
   <a class="Left" href="../index.html">&uarr; 2013 &uarr;</a>
-  <a class="Left Disabled" href="#">last entry</a>
+  <a class="Left" href="../../2014/birken/index.html">2014/birken &rarr;</a>
   <a class="Right" href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2013/robison/robison.c">C code</a>
   <a class="Right" href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/2013/robison/Makefile">Makefile</a>
   <a class="Right" href="#inventory">Inventory</a>
   <a class="Right" href="https://validator.w3.org/nu/?doc=https%3A%2F%2Fioccc-src.github.io%2Ftemp-test-ioccc%2F2013%2Frobison%2Findex.html">&#x2713;</a>
 </div>
 
-<!-- END: this line ends content from: inc/navbar.last.html -->
+<!-- END: this line ends content from: inc/navbar.mid.html -->
 <!-- START: this line starts content from: inc/before-content.default.html -->
 
     <div class="content" id="content">