Refactored monos, added many features to posys

 - Created a template 'nomials' class for shared features
 - added 'eid' attribute to monomials (it's basically a hash of 'exp')
 - added algebraic simplification to both monomials and posynomials
 - added posynomial-posynomial multiplication
would it make any sense to compare eid's now that we have them, instead of using str()?