Bayesian-optimization

Two new features are included in this release:
1. [Kappa decay](https://github.com/fmfn/BayesianOptimization/pull/224): Allows for dynamical changing the balance between exploration and exploitation during the optimization process (when using UCB).
2. [Sequential domain reduction](https://github.com/fmfn/BayesianOptimization/pull/226): Ability to zoom-in promising regions in the search space for faster convergence.

This release is brought to you by:
1. [ben-arnao](https://github.com/ben-arnao)
2. [osullivryan](https://github.com/osullivryan)

Latest release included changes to `Events.OPTIMIZATION_STEP` that were worthy of a minor version bump.

This release simplifies the proxy search making the process faster.

This release comes with a number with small fixes (typos and etc.) as well as more tests.

Big refactor with a few API breaking changes.

Thanks to Erotemic for his contributions.