Define a command-line switch that silences non-essential stdout chatter, if desired

[axch]

Said chatter would be

• The progress reports called for by #13
• The start/stop notifications
• Possibly some of the warnings (not errors) detailed in #45

Implementation options:

• Teach the core to accept command-line or environment-variable arguments for items like this that do not affect model output, or
• Add yet another item to the parameter file.

The Python driver program can translate its own command-line switches to whichever of these methods is chosen.