Chess variant puzzle generator

This is a simple puzzle generator for chess variants based on Fairy-Stockfish and its python binding pyffish.

Generating puzzles in PGN format currently consists of running the following scripts

1. generator.py to generate a set of FENs.
2. puzzler.py to identify puzzles within those FENs and store them as EPD. This step can be run on the EPD to re-evaluate the puzzles, e.g., at higher depth.
3. pgn.py to convert the EPD to a PGN.