Added missing predict_proba() and predict_log_proba() to MultinomialNb

[kakserpom]

Related to #183

[codecov]

Codecov Report

Attention: Patch coverage is 33.33333% with 20 lines in your changes missing coverage. Please review.

Project coverage is 35.62%. Comparing base (5272ad1) to head (503753a).

Files with missing lines	Patch %	Lines
algorithms/linfa-bayes/src/multinomial_nb.rs	33.33%	20 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #385      +/-   ##
==========================================
- Coverage   35.90%   35.62%   -0.28%     
==========================================
  Files          97       97              
  Lines        6409     6439      +30     
==========================================
- Hits         2301     2294       -7     
- Misses       4108     4145      +37     

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