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/pearl.html

@@ -0,0 +1,13 @@
+Pearl
+<p>
+Draw a single closed loop by connecting together the centres of
+adjacent grid squares, so that some squares end up as corners, some as
+straights (horizontal or vertical), and some may be empty. Every
+square containing a black circle must be a corner not connected
+directly to another corner; every square containing a white circle
+must be a straight which is connected to <em>at least one</em> corner.
+<p>
+Drag between squares to draw or undraw pieces of the loop.
+Alternatively, left-click the edge between two squares to turn it on
+or off. Right-click an edge to mark it with a cross indicating that
+you are sure the loop does not go through it.