control: ability to roundtrip partial control files

[jmccreight]

A concrete instance:
prms_warmup option has default of zero (in 5.2.1) but the default in pyPRMS is set 1. I have a control file without prms_warmup, round tripping the file causes output differences in the runs for runs longer than one year.

It sounds like updating the default in pyPRMS to the value in 5.2.1+ is good.

I see why populating all the control variables is desirable but it is also desirable to be able to roundtrip partial/incomplete control files. An option to do complete or maybe roundtrip mode on .init() could simply collect the keys and then delete these from the Control object before returning.

[pnorton-usgs]

@jmccreight - I have created a branch https://github.com/DOI-USGS/pyPRMS/tree/control_default_values_PAN that adds the ability to not pre-populate the Control class with all valid control variables. A new argument, include_missing was added to Control and ControlFile. The default behavior when instantiating a Control object is to pre-propulate the object with all valid control variables. The default when instantiating a ControlFile object is to create an empty Control object so you shouldn't have to change your code to just get the control variables from a control file.

Could you try this branch out and see if it meets your needs?