Standard optimization test functions

[alejandrom247]

I want to implement a series of test functions to validate the performance of the optimization algorithms used in the dnn_opt library.

[jairodelgado]

I would suggest being explicit about the test functions you want to implement, I think these shuould suffice for this issue:

• 25. Brown Function
• 34. Chung Reynolds Function
• 38. Cosine Mixture Function
• 40. Csendes Function
• 43. Deb 1 Function
• 44. Deb 3 Function
• 48. Dixon & Price Function
• 53. Egg Holder Function
• 54. Exponential Function
• 57. Giunta Function

Each function specification can be found in: http://arxiv.org/abs/1308.4008v1

Also let's limit the scope of this issue to sequential implementation in the core layer.

[jairodelgado]

As the number of benchmark functions is growing, in order to keep the code organized we are creating a new namespace within solutions (dnn_opt::core::solutions::bench). A corresponding folder has been created to this end. See b5cbe90 and f46bbbe.