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/range.html

@@ -0,0 +1,21 @@
+Range
+<p>
+Colour some squares black, so as to meet the following conditions:
+<ul>
+<li>
+No two black squares are orthogonally adjacent.
+<li>
+No group of white squares is separated from the rest of the grid by
+black squares.
+<li>
+Each numbered cell can see precisely that many white squares in
+total by looking in all four orthogonal directions, counting itself.
+(Black squares block the view. So, for example, a 2 clue must be
+adjacent to three black squares or grid edges, and in the fourth
+direction there must be one white square and then a black one beyond
+it.)
+</ul>
+
+<p>
+Left-click to colour a square black. Right-click to mark a square
+with a dot, if you know it should not be black.