Add bernoulli naive bayes implementation

[relf]

This PR supersedes #242

Moreover, NaiveBayes trait is made public as suggested in this comment and provides sklearn-like methods predict_log_proba() and predict_proba() as mentioned in this comment

This PR resolves #183 and also supersedes #385

[codecov]

Codecov Report

Attention: Patch coverage is 42.74194% with 71 lines in your changes missing coverage. Please review.

Project coverage is 36.03%. Comparing base (5272ad1) to head (f73bb74).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
algorithms/linfa-bayes/src/bernoulli_nb.rs	47.72%	23 Missing ⚠️
algorithms/linfa-bayes/src/hyperparams.rs	12.00%	22 Missing ⚠️
algorithms/linfa-bayes/src/lib.rs	55.55%	12 Missing ⚠️
algorithms/linfa-bayes/src/base_nb.rs	42.10%	11 Missing ⚠️
algorithms/linfa-bayes/src/multinomial_nb.rs	57.14%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #388      +/-   ##
==========================================
+ Coverage   35.90%   36.03%   +0.13%     
==========================================
  Files          97       99       +2     
  Lines        6409     6502      +93     
==========================================
+ Hits         2301     2343      +42     
- Misses       4108     4159      +51     

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