Implement hyperbolic functions and their inverses

[lakshayg]

CNTK currently does not have the following functions

• Sinh
• Cosh
• Asin
• Acos
• Asinh (PR Sent)
• Acosh (PR Sent)
• Atanh (PR Sent)

Some of them can be useful as activation functions (http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.10.6514&rep=rep1&type=pdf). I would like to implement this functionality in CNTK. Before starting with the implementation, I would like to have some feedback.

[ishikasoni]

Can I work on implementing acosh

[lakshayg]

@ishikasoni Sure! go ahead.