This completely removes the old system of mkfiles.pl + Recipe + .R
files that I used to manage the various per-platform makefiles and
other build scripts in this code base. In its place is a
CMakeLists.txt setup, which is still able to compile for Linux,
Windows, MacOS, NestedVM and Emscripten.

The main reason for doing this is because mkfiles.pl was a horrible
pile of unmaintainable cruft. It was hard to keep up to date (e.g.
didn't reliably support the latest Visual Studio project files); it
was so specific to me that nobody else could maintain it (or was even
interested in trying, and who can blame them?), and it wasn't even
easy to _use_ if you weren't me. And it didn't even produce very good
makefiles.

In fact I've been wanting to hurl mkfiles.pl in the bin for years, but
was blocked by CMake not quite being able to support my clang-cl based
system for cross-compiling for Windows on Linux. But CMake 3.20 was
released this month and fixes the last bug in that area (it had to do
with preprocessing of .rc files), so now I'm unblocked!

CMake is not perfect, but it's better at mkfiles.pl's job than
mkfiles.pl was, and it has the great advantage that lots of other
people already know about it.

Other advantages of the CMake system:

 - Easier to build with. At least for the big three platforms, it's
   possible to write down a list of build commands that's actually the
   same everywhere ("cmake ." followed by "cmake --build ."). There's
   endless scope for making your end-user cmake commands more fancy
   than that, for various advantages, but very few people _have_ to.

 - Less effort required to add a new puzzle. You just add a puzzle()
   statement to the top-level CMakeLists.txt, instead of needing to
   remember eight separate fiddly things to put in the .R file. (Look
   at the reduction in CHECKLST.txt!)

 - The 'unfinished' subdirectory is now _built_ unconditionally, even
   if the things in it don't go into the 'make install' target. So
   they won't bit-rot in future.

 - Unix build: unified the old icons makefile with the main build, so
   that each puzzle builds without an icon, runs to build its icon,
   then relinks with it.

 - Windows build: far easier to switch back and forth between debug
   and release than with the old makefiles.

 - MacOS build: CMake has its own .dmg generator, which is surely
   better thought out than my ten-line bodge.

 - net reduction in the number of lines of code in the code base. In
   fact, that's still true _even_ if you don't count the deletion of
   mkfiles.pl itself - that script didn't even have the virtue of
   allowing everything else to be done exceptionally concisely.

It isn't necessary to cause the right files to _exist_, because
makedist.sh is run from Buildscr which has already run mkauto. But it
turns out it _is_ important to get the relative timestamps of
Makefile.in and Makefile.am the right way round, otherwise somebody
who unpacks the tarball and runs 'configure' and 'make' will find make
tries to rebuild Makefile.in because it thinks Makefile.am is newer -
and if they don't have the right automake installed, or any automake,
that will fail.

A load of source files in the icons subdirectory were being left out
of the distribution tarball because I tried to include them using a
combined wildcard and bash brace expansion - but makedist cites
/bin/sh, so can't get away with bashisms. Expanded the braces.

A long time ago, it seemed like a good idea to arrange that binaries
of my puzzles would automatically cease to identify themselves as a
particular upstream version number if any changes were made to the
source code, so that if someone made a local tweak and distributed the
result then I wouldn't get blamed for the results. Since then I've
decided the whole idea is more trouble than it's worth, so I'm
retiring it completely.

[originally from svn r10264]

I'm going through all my projects and reworking them to avoid
depending on the monotonic integer-valued source control revision
identifier provided by Subversion, so I can migrate everything to git
without my builds and versioning breaking.

Puzzles's version number is now of the form YYYYMMDD.vvvvvv, where
vvvvvv is some string of source control information (currently still
the SVN-style "rNNNNN", but free to change in future). The date
provides monotonicity between my official automated builds, and the
second component is the one I'll be most interested in when people
send bug reports.

[originally from svn r10263]

Makefile.am, and there's a new mkauto.sh which builds a corresponding
configure script.

The old makefile has been renamed from 'Makefile' to 'Makefile.gtk',
indicating that the intended new _default_ approach is to use the
autoconf world. Makefile.gtk is provided as an emergency fallback in
case anything fails with the new stuff that used to work with it.

The new configure script does not support the same $(BINPREFIX) system
as the old Makefile did. However, as I understand it, it should be
possible to configure using --program-prefix="sgt-" (for example) and
then the binaries should all be renamed appropriately at install time.

The Makefile.am is quite painful. The Puzzles codebase relies heavily
on compiling individual object files multiple times with different the
cpp flags per build deliverable (program or library) and not per
source file. Solution: anything built with non-default compile options
has to go in its own little library. But that doesn't work either in
the general case, because as soon as you have more than one such
library linked into an application, Unix ld semantics bite you if the
objects in the libraries both refer to each other. So I ended up
building all those little libraries but not _using_ them - instead the
link commands for the programs needing those objects refer to the
objects directly, under the silly names that automake gives them.
(That's less fragile than it sounds, because it does _document_ the
names of the intermediate object files. But still, yuck.)

[originally from svn r9886]

[originally from svn r7600]

re-run of mkfiles.pl to fail.

[originally from svn r7567]

infrastructure to the mkfiles.pl framework for the convenience of
the build script: it generates `wingames.lst', a list of the Windows
binaries which are ship-worthy games as opposed to nullgame or
command-line auxiliary programs.

[originally from svn r7206]

[originally from svn r7025]