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/unruly.html

@@ -0,0 +1,12 @@
+Unruly
+<p>
+Colour every square either black or white, in such a way that:
+<ul><li>no three consecutive squares, horizontally or vertically, are
+the same colour
+<li>each row and column contains the same number of black and white
+squares.</ul>
+<p>
+Left-click in an empty square to turn it black it out, or right-click
+to turn it white. Click again in an already-filled square to cycle it
+between black and white and empty; middle-click to reset any square to
+empty.