Overhauls function naming to be more verb-centric a la tidy convention
Removes some unused / not useful functions
Adds significant test coverage hitting the actual API, since it turns out that Fitbit's example API responses in their docs don't actually match what the API gives back...
Improves error messaging by trying to parse JSON messages in a custom stop_for_status() implementation
Adds some new methods for intraday time series (i.e. your heart rate every 1 minute for a day)