Add "only_best_status" option to Persist

[TsumiNa]

This option enables Persist to only save the best states of each criterion

[codecov[bot]]

Codecov Report

Merging #233 (48074c4) into master (d504a1f) will increase coverage by 58.02%. The diff coverage is 75.00%.

@@             Coverage Diff             @@
##           master     #233       +/-   ##
===========================================
+ Coverage   35.46%   93.49%   +58.02%     
===========================================
  Files          95       26       -69     
  Lines        6868     2644     -4224     
===========================================
+ Hits         2436     2472       +36     
+ Misses       4432      172     -4260     

Impacted Files	Coverage Δ
tests/models/test_extension.py	94.73% <75.00%> (-3.81%)	:arrow_down:
...riptors/descriptor/frozen_featurizer_descriptor.py
xenonpy/contrib/ismd/reactant_pool.py
xenonpy/utils/math/__init__.py
xenonpy/model/sequential.py
xenonpy/utils/useful_cls.py
xenonpy/model/training/base.py
xenonpy/model/nn/wrap.py
xenonpy/model/utils/__init__.py
xenonpy/_conf.py
... and 59 more

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[TsumiNa]

@stewu5 Could you please check the docs for the new option? Also, the codes if you have any comment.