I don't necessarily think all of these make the code better or easier to read, but it's easier to just go along with what the tools want, since they do generally make things better.
There should be no functional changes here.
This brings most of the history-related functionality implemented in the grpc scripts to the JSON version, but only for text output. It also renames parserJsonHistory.py to dish_json_text.py, which removes the last remaining complaint from pylint about module name not conforming to style conventions.
A lot of this is just duplicated code from dish_common and dish_grpc_text, just simplified a little where some of the flexibility wasn't needed.
This removes compatibility with Python 2.7, because I didn't feel like reimplementing statistics.pstdev and didn't think such compatibility was particularly important.
