puzzles/unfinished

This subdirectory contains puzzle implementations which are
half-written, fundamentally flawed, or in other ways unready to be
shipped as part of the polished Puzzles collection.

The CMake build system will _build_ all of the source in this
directory (to ensure it hasn't become unbuildable), but they won't be
included in all-in-one puzzle binaries or installed by 'make install'
targets. If you want to temporarily change that, you can reconfigure
your build by defining the CMake variable PUZZLES_ENABLE_UNFINISHED.
For example,

  cmake . -DPUZZLES_ENABLE_UNFINISHED="group;slide"

will build as if both Group and Slide were fully official puzzles.