Serialization does not produce a valid SBML

[carrascomj]

There is no xml header and probably the namespaces in the <model> are wrong. This makes it impossible to read models serialized with rust_sbml through libSBML, which is a big flaw.

There are other problems that may make a model readable through rust_sbml but not libSBML like identifier uniqueness through Species and Reaction that rust_sbml does not check at all. There may opportunities for validation/automatic correction in the future.