Calculate average download rate the same way as downloadrate
Add config option for choosing which nzbget variables to monitor, and provide a default
Pep8 fixes
Refactoring and changes based on @balloob's comments
Add nzbget.py to .coveragerc omit list. Check if there are any http
errors (like bad auth) when creating the nzbgetapi class. If there
are, the setup_platform() function will return false. Exceptions are
logged as well.
When a new sensor is created, assign the initial value from the api
instead of simply using None until the first update call.
