PAT 2.0 - Add internationalization documentation

[DavidGoldwasser]

This will support both units and language preferences. It will impact what units input arguments are flagged as, the language for argument descriptions. It will also affect unit conversions and log messages in the run section.

@macumber do you think the Name, Description, and Modeler Descriptions section should support internationalization. If that is the case, we would need to have runner passed in to them. It also opens a can of worms about the XML file? Is that better left not open. (Update: ok, so arguments go into xml as well so we are already going to have to address how that happens)

My plan is to create a new section in Advanced Topics to document internationalization. The basic measure example won't show this. The implementation of internationalization should allow existing measure stock to work as is without any changes.