Tests in python3.
More general Pow method.
Redid differentiation.
Added some very basic simplifications of the expressions.
Better formatting of expression prints.
Removed subtraction and division objects in favor of inverse and negation.
Allowing more specific optimizations of expressions.
Changed the expression api closer to the way it was before.
Never going back to python2!
Getting the solver to work with the changed expressions code.
Sum of powers when multiplying identical terms.
Removed the _Neg expression, negation is now multiplication by -1.
Printing constraints derivations in solver.
Optimizations of addition.