Introduce a mechanism in this source tree for building the container

web pages for the Java applets. Previously, those have all been
maintained by hand in my website's svn area, which is a bit silly. Now
we have a file per puzzle in the 'html' subdirectory which contains
the puzzle's name, one or two attributes, and the instructions snippet
to go below the puzzle applet; and then there's a Perl script that
builds all the real web pages out of that by adding in the parts
common across all files: the header, footer, and middle fragment with
the <applet> tag and resizing bits and pieces.

One piece _not_ checked in here is the footer text specific to my
hosting at chiark, which I think does still belong in the www area. So
Buildscr doesn't actually build the web pages; it just delivers the
bits and pieces by which my nightly snapshot script will be able to
run the program that _does_ build them, passing that footer as an
extra argument.

[originally from svn r9780]

html/lightup.html

@@ -0,0 +1,10 @@
+Light Up
+<p>
+Place light bulbs in the grid so as to light up all the blank
+squares. A light illuminates its own square and all the squares in
+the same row or column unless blocked by walls (black squares).
+Lights may not illuminate each other. Each numbered square must be
+orthogonally adjacent to exactly the given number of lights.
+<p>
+Click on a square to place or remove a light. Right-click to place a
+dot indicating that you think there is no light in that square.