Implement more symbolic functionality

[tpfto]

Some other planned symbolic functionality I hope to implement in the near future include the following:

1. Interconversion between Carlson integrals and the Legendre-Jacobi integrals (EllipticF[], EllipticE[], ElllipticPi[], EllipticK[]).

2. Further calculus support (integration of elliptic integrals, limits, series expansions, etc.)

3. Implement simplification identities with functions already in Mathematica (e.g. elliptic functions, theta functions) for FunctionExpand[]/FullSimplify[].

Other suggestions for added symbolic functionality are welcome.