Add several global optimization algorithms

[gaetanserre]

Implements several global optimization algorithms:

• Pure Random Search
• LIPO (Global optimization of Lipschitz functions, Malherbe et al. 2017)
• RankOpt (A Ranking Approach to Global Optimization, Malherbe et al. 2017)

Define the evalEnv environment : a stationary environment where the reward is given by evaluating a fixed measurable function at the chosen action.

Prove that PRS is consistent.

[RemyDegenne]

Can you place the algorithms under Optimization/Algorithms/ ? Except for PRS, which is much more general than optimization and should go to SequentialLearning/Algorithms. Also the S in PRS is application-specific since it means search, but that algorithm can also be used for non-search applications, so another name for PRS would be better. What about randomSampling?

[gaetanserre]

Indeed randomSampling is nice. I renamed PRS.

[RemyDegenne]

Can you open a new PR for the EvaluationEnv file only?

[gaetanserre]

See #98.