The IntPower class has been renamed from ConstPower, breaking the API. A TermPower class was added. A division operator was added. User defined nary functions are now provided in addition to unary and binary functions. Evaluation of gradients using a subset of the variables was implemented. This is used for parameterized functions having "constant" parameters in addition to the actual function argument. Power terms can now have terms in the exponent, in addition to constants.
