* Trend sensor now uses linear regression to calculate trend
* Added numpy to trend sensor test requirements
* Added trendline tests
* Trend sensor now has max_samples attribute
* Trend sensor uses utcnow from HA utils
* Trend sensor now completes setup in async_added_to_hass
* Fixed linter issues
* Fixed broken import
* Trend tests make use of max_samples
* Added @asyncio.coroutine decorator to trend update callback
* Update trend.py