Added exp(-x) to the flist(sin, cos, sinh, cosh has the same canonical form for f(x) and f(-x) while exp doesn't). Also, added a test in bch_expansion to decide whether expansion_search should look for series expansion in I*x or x
Now works for squeezing operators with real parameters, even with r*exp(I*theta) form. But needs improvement with finding terms including Imaginary numbers. Passed all tests in the notebook
removed debug prints
Merge pull request #4 from eunjongkim/expansion_search

Expansion search
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