Added sech and csch under ReciprocalHyperbolic class

Definitions of csch, asech and acsch will follow in further commits.
On Wed, Dec 10, 2014 at 06:47:51AM -0800, Shivam Vats wrote:
>    I don't know.

Probably, due to review.  You can just read
the pr history, but it seems to be difficult in this case
due to the size.