Add units and new mathML to reserved words list

[luciansmith]

Units like 'length' and 'volume' need to be added to the reserved words list, so we properly translate models coming in from SBML. Similarly, l3v2 mathML like 'max' and 'min' are effectively reserved words, too. Need to add them to the reserved words list and make sure this doesn't affect other behavior (such as normal l3v2 models with 'max' and 'min').

Reported by: luciansmith