Improve the puzzle index functionality so other features can be implemented

[Siderite]

• limit the memory usage by dynamically recreating the map required for operations or directly reading from the file with binary search (which should be very slow, but use no memory)
• compress the FEN before processing and decompress it afterwards?
  • this would increase the number of possible 3-grams, making the file larger
• can we index the individual positions, number those, and associate arrays of these ids with a puzzle id?
• test using variable N for the N-grams: 3-grams for most stuff, 4 and larger to capture the too common 3-grams or lesser.
  • this implies upgrading the NIF format
  • which should also be formalized and blogged
• also add the possibility of adding multiple types of data for the same element, like checksums together with n-grams or n-grams applied on different text representations of the same thing.