Import a CRN encoded in SBML format

[EricESeverson]

SBML is a standard encoding for models of biological processes.
http://sbml.org/Main_Page

It supports a lot more features than just a basic CRN, but if something is encoded that is a pure CRN (with 1->1 and 2->2 reations), it should be able to import directly to ppsim.

The following repository has hundreds of real models in the SBML language.
https://www.ebi.ac.uk/biomodels/
We should see if any of these examples could be faithfully simulated by ppsim.