major rewrite of data element handling

Borrowing a bit from https://github.com/mooseman/pd_curses_stuff/ -- This adds a Controls module with Gauge as a class. Instantiate a display of a bit of data once, hang on to the handle, and call .update(value) for automagic awesome. Gauge instance provides neat things for free like last updated time and min/max values. Subclass it to add a history FIFO (to compute mean/avg values) or (my master plan) ascii minicharts/sparklines.