Error function: x -> erf(x)

::

 erf(float x) -> float
 erf(DM x) -> DM
 erf(SX x) -> SX
 erf(MX x) -> MX

Extra doc: https://github.com/casadi/casadi/wiki/L_pm

Doc source: https://github.com/casadi/casadi/blob/develop/casadi/core/generic_expression.hpp#L542

Implementation: https://github.com/casadi/casadi/blob/develop/casadi/core/generic_expression.hpp#L542-L544

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