allow short name alternatives for setting fields from command line

[tmchartrand]

Seems like it would be fairly straightforward to add the option of setting short names for fields to make them easier to specify from the command line ("-i" vs "--input"), unless I'm missing something and this is already possible?
If this would make sense to include I'd be glad to test something out and file a PR at some point.

[fcollman]

So the only problem here is when you have nested inputs, it's not obvious how to handle those, and you have to make sure that you aren't repeating keys across things. You could try though just adding in some extra metadata to the fields, and then modifying the argparse constructor. One thing to watch out for would be if you had someone specify a short_name that conflicts with a long name. (particularly across potentially nested parameters).