Nonlinear / linear constraints

[Balaji Pokuri]

Current constraints are limited to upper and lower bounds., However other constraints (linear/non-linear) maybe needed depending on the problem. These should be checked in the surrogate optimizer, to prevent sampling in those regions.

[Baskar Ganapathysubramanian]

Low Priority until Dec 2017

[Alec Lofquist]

Added to find_next_query_point in ad377a43, but constraints are not yet considered during init_strategy.

[Alec Lofquist]

Added to acquisition function in 311da022a, still not really tested