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/solo.html

@@ -0,0 +1,20 @@
+Solo
+<p>
+Fill in a number in every square so that every number appears
+exactly once in each row, each column and each block marked by thick
+lines.
+<p>
+To place a number, click in a square to select it, then type the
+number on the keyboard. To erase a number, click to select a square
+and then press Backspace.
+<p>
+Right-click in a square and then type a number to add or remove the
+number as a pencil mark, indicating numbers that you think
+<em>might</em> go in that square.
+<p>
+When you master the basic game, try Jigsaw mode (irregularly shaped
+blocks), X mode (the two main diagonals of the grid must also
+contain every number once), Killer mode (instead of single-cell
+clues you are given regions of the grid each of which must add up to
+a given total, again without reusing any digits), or all of those at
+once!