funman changes

[mwdchang]

Summary

• Add a compartmental sanity check (mass conservation + non-negativity), this is turned on by default
• Lower the default tolerance value, 0.89 was too high and we almost always need to lower it
• Add calculation for normalization constant = sum(eval(initial state expressions))

Testing

Maybe a bit difficult as funman had not been stable since last sync against their develop-branch. Probably want to use simple models like SIR.

[YohannParis]

LGTM