Upgrade language is inconsistent

In the Developer's Guide we describe two kinds of upgrade, "full" and "soft". I think we used to use the terms "hard" and "soft", and "hard" was changed to "full" to provide a more accurate description of what happens. There are still a few leftover occurrences of "hard" in the docs here and there.

However, "soft" doesn't provide much indication of what happens in that kind of upgrade. Would "partial" be more correct? If not, is there a good alternative?

I can go through the docs and fix the language based on whatever you all think makes sense.