Fix nb_gm_003 and improve it with chunk-by-chunk sequence generation. It's now non-skewed and number of matches is controlled for a sequence.

import nb_gm_004 from progressive randomizer

Implement nb_gm_001, nb_gm_002, nb_gm_003, nb_gm_004, and benchmarks for all of them plus progressive randomizer

fix skewed random generator, so it generates skewed sequences! It also calculates skewness as described in Ralph (2014, p.21).

PEP8 conformity and improve readability in progressive random sequence generator.

generate skewed data for stat analysis.

refactors, add normalized cost functions to progressive n-back, and a new demo for progressive n-back.