Chopin2

Round the accuracy up to three decimal places.

This release integrates the following changes:

- Code refactoring of `chopin2.py` and `functions.py`;
- Fix a minor bug about the processing order of features combinations with the same group size.

This releases fixes a major bug in the generation of random level vectors.
Using previous versions of *chopin2* is highly discouraged!

A few minor improvements and fixes

Improving performances on the generation of the HD model.
Use the same training/test configuration for each run of percentage-split and k-fold cross-validation in --select_features mode

Supporting k-fold cross-validation