Added sech and csch under ReciprocalHyperbolic class

Definitions of csch, asech and acsch will follow in further commits.
On Wed, Dec 10, 2014 at 06:11:21AM -0800, Shivam Vats wrote:
>    I couldn't think a problem with this attribute as no one pointed anything
>    out here: [2]#7606

That pr was closed, isn't?