Issue 144 add machine learning challenges

[pvk-developer]

• Implement from_dict for the Tunable class.
• Improved benchmark function.
• Created MLChallenge.
• Implemented CensusRF challenge, based on `MLChallenge.
• Included a .tar.gz file with Census data in order to not depend on external resources (links).
• Updated HyperParameters to have a default value that can be set by the user or autogenerated.
• Updated tests.
• Resolve #144
• Resolve #150
• Resolve #151
• Resolve #152

[codecov-io]

Codecov Report

Merging #149 into master will increase coverage by 0.07%. The diff coverage is 95.03%.

@@            Coverage Diff             @@
##           master     #149      +/-   ##
==========================================
+ Coverage   94.38%   94.45%   +0.07%     
==========================================
  Files          35       36       +1     
  Lines         694      793      +99     
==========================================
+ Hits          655      749      +94     
- Misses         39       44       +5

Impacted Files	Coverage Δ
btb/benchmark/tuners/btb.py	0% <0%> (ø)	:arrow_up:
btb/benchmark/challenges/bohachevsky.py	100% <100%> (ø)	:arrow_up:
btb/benchmark/challenges/rosenbrock.py	100% <100%> (ø)	:arrow_up:
btb/benchmark/challenges/__init__.py	100% <100%> (ø)	:arrow_up:
btb/benchmark/challenges/census.py	100% <100%> (ø)
btb/tuning/hyperparams/base.py	95.23% <100%> (+0.07%)	:arrow_up:
btb/tuning/hyperparams/numerical.py	88.88% <100%> (+1.01%)	:arrow_up:
btb/benchmark/challenges/branin.py	100% <100%> (ø)	:arrow_up:
btb/tuning/hyperparams/categorical.py	94.11% <100%> (+0.56%)	:arrow_up:
btb/tuning/hyperparams/boolean.py	95.23% <100%> (+0.5%)	:arrow_up:
... and 4 more

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