Pass temperature as command line arg

This enhancement will make it easier to script for large numbers of simulations as you don't have to open up main.cpp to modify the model.

Start with main.cpp and identify where the simulation temperature is currently configured. Make the temperature configurable through a command-line argument so scripts can run different simulations without editing main.cpp; verify the program still runs with the argument provided.

Written by the indexing model from the issue text.