Eliminate NPcore.Rdata

[mnneely]

I'd like to get rid of NPcore.Rdata and just use PMout.Rdata. The structure of both files is similar enough that any remaining differences can be harmonized, and we run into errors saving a PM_result object when it is rust, i.e. PM_result$save(). It doesn't save correctly, and this problem can be eliminated by always using PMout.Rdata as the save object. They can be loaded exactly the same way in PM_load, and if needed we can always check for the $NPdata$backend flag to know what the engine was, making the differential file naming redundant.

I've fixed the problem for now by having PM_load use the Out2List() function for both objects. If you want details, the $save function saves a list called PMout back to the PMout.Rdata or NPcore.Rdata file. However, PM_load was only using get("NPcore") after loading the file, and that did not exist because the list was called PMout, not NPcore. Out2List works because it agnostically cycles through the list objects returned after loading and doesn't get them by name.

Not to mention that we've also changed to PMcore anyway.

[mhovd]

Is this still an issue?