one hot encoder

[ksaur]

scikit-learn one-hot-encoder impl
Scikit learn had API change that removed categorical_features, complicating things a bit

[codecov-commenter]

Codecov Report

Merging #193 into master will increase coverage by 0.06%.
The diff coverage is 95.02%.

@@            Coverage Diff             @@
##           master     #193      +/-   ##
==========================================
+ Coverage   93.72%   93.79%   +0.06%     
==========================================
  Files          28       30       +2     
  Lines        1609     1772     +163     
  Branches      284      314      +30     
==========================================
+ Hits         1508     1662     +154     
  Misses         58       58              
- Partials       43       52       +9     

Flag	Coverage Δ
#unittests	93.79% <95.02%> (+0.06%)	⬆️

Impacted Files	Coverage Δ
hummingbird/ml/operator_converters/skl_iforest.py	90.21% <90.21%> (ø)
hummingbird/ml/_container.py	96.72% <100.00%> (+0.56%)	⬆️
hummingbird/ml/_topology.py	90.90% <100.00%> (+0.34%)	⬆️
hummingbird/ml/operator_converters/__init__.py	100.00% <100.00%> (ø)
...mmingbird/ml/operator_converters/_base_operator.py	100.00% <100.00%> (ø)
...rd/ml/operator_converters/_tree_implementations.py	98.08% <100.00%> (+0.05%)	⬆️
hummingbird/ml/operator_converters/constants.py	100.00% <100.00%> (ø)
...bird/ml/operator_converters/skl_one_hot_encoder.py	100.00% <100.00%> (ø)
hummingbird/ml/supported.py	88.70% <100.00%> (ø)
... and 1 more

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[interesaaat]

Ok I added few comments. Will merge once all checks pass

[interesaaat]

Closes #136.