return 1 for z=0 early in _hyperexpand()
Implement series expansion for elliptic_e(z) and elliptic_k(z)
Fixed apparent bug at hyperexpand_special
elliptic_integrals.py: More short doctests for series + regular tests for series
Merge pull request #2327 from skirpichev/elliptic-hyper

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