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/bridges.html

@@ -0,0 +1,13 @@
+Bridges
+<p>
+Draw horizontal or vertical bridges to link up all the islands.
+Bridges may be single or double; they may not cross; the islands
+must all end up connected to each other; the number in each island
+must match the number of bridges that end at that island (counting
+double bridges as two). Note that loops of bridges are permitted.
+<p>
+Click on an island and drag left, right, up or down to draw a bridge
+to the next island in that direction. Do the same again to create a
+double bridge, and again to remove the bridge if you change your
+mind. Click on an island without dragging to mark the island as
+completed once you think you have placed all its bridges.