when this documentation was re-written, it was done incorrectly. this corrects that and also removes \mathrm{}
also \mapsto is more correct than \rightarrow here
don't use \mathrm{} on d in differentials in latex
in sympy documentation, don't use \mathrm{} where we mean \operatorname;
in documentation, don't use \mathrm{} on d in derivatives and integrals
in documentation, prefer \Im and \Re to \mathrm{Im} and \mathrm{Re}
in mpmath code, correct some latex markup in documentation