enable configurable puzzle difficulty. I'm only generating grids up
to Times level (complicated non-recursive analysis but guessing
never required); I wouldn't object to providing a Telegraph
difficulty level (guessing required) but it turns out to be very
hard indeed to generate at random. I might still add it later
(probably under the name `Unreasonable' :-) if I can think of an
efficient way to find them.
[originally from svn r5682]
- added a compilation option -DSTANDALONE_SOLVER which makes both
of Solo's internal solvers accessible from the command line.
- fix a bug in nsolve turned up by testing in this mode: it failed
to iterate at all! Oddly, this massive improvement to the
effectiveness of nsolve hasn't emptied the generated grids by
very much.
- add an extra mode of reasoning to my to-do list (which is the
dual of one already there, so I'm kicking myself).
[originally from svn r5670]
the default symmetry from order-4 down to order-2, which seems to
mitigate the excessively-full-grid problem by permitting more
freedom to remove stuff.
[originally from svn r5666]
