Cyeva

Fix
* 36
* pint warnings
* typo

add some calc_threshold* method to Compare object

Features
* calc_mbe: mean bias error
* calc_threshold_hit_ratio

Fix
* drop_nan: The problem that if input as list, the result is unexpect.

Tests
* add test for:
* calc_mae
* calc_mbe
* calc_threshold_hit_ratio
* calc_threshold_false_alarm_ratio
* calc_threshold_ts
* calc_linregress

fix: wind direction identification incorrect problem.