Idea for fitting process file naming

[taldcroft]

One idea for unifying the fitting process is to default to an input model spec file name of '{}_model_spec.json'.format(model_name). So basically it reads the flight model spec by default.

Next, the write method would default to using the same file name for output, but just before overwriting it will make a backup of the original, like pftank2t_model_spec.json-01. The final two digit number would be determined as the first available two digit number, so you might have pftank2t_model_spec.json-12 after a while. These would be easy to clean out when all is done.

As an aside, one might settle on a standard short name, e.g. xf for the XijaFit object in the production fit scripts in chandra_models. Then all the scripts have a more similar look and feel, and it's easier to adapt an existing script for a new model.

[matthewdahmer]

hmm, this might be cleaner than using dates (which are already included as an attribute of the file anyway, unless they are copied or manually changed). I like the xf suggestion.