added SymEq for unevaluated symbolic equalities
worked with eunjong on refactoring series expansion search code
Merge pull request #5 from jrjohansson/symeq

added SymEq for unevaluated symbolic equalities
Merge pull request #6 from jrjohansson/series-expansion-search-refactoring

worked with eunjong on refactoring series expansion search code
fixed a bug that fails to find expansion for unitary_transformation(U, sy)