Implement series expansion for elliptic_e(z) and elliptic_k(z)

This pull also adds auto evaluation: hyper([a1,..,ap], [b1,..,bq], 0) = 1, see [this](http://functions.wolfram.com/HypergeometricFunctions/HypergeometricPFQ/03/01/01/).  Maybe we should check for R of convergence?