Idiomaticize

Here are some (independent) commits that make some idiomaticizing changes to gmond_exporter. Choose any/all/none as it pleases you.

Probably you'd be better served using a time.Ticker in your main loop, but I believe that would require a bit of restructuring of that select statement, which I would attempt to solve if you had any interest in seeing it.

Also, I think there may be synchronization issues around the gaugePerGangliaMetrics writes, but solving that would likely best be accomplished with a rather thorough refactoring, to remove the global state altogether.