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/guess.html

@@ -0,0 +1,12 @@
+Guess
+<p>
+Try to guess the hidden combination of colours. You will be given
+limited information about each guess you make, enabling you to
+refine the next guess.
+<p>
+Drag from the colours on the left into the topmost unfilled row to
+make a guess; then click on the small circles to submit that guess.
+The small circles give you your feedback: black pegs indicate how
+many of the colours you guessed were the right colour in the right
+place, and white pegs indicate how many of the rest were the right
+colours but in the wrong place.