move file with class 'ARIANEapproach' to approaches folder

tas/approaches/__init__.py

+from _ariane import ARIANEApproach
+
+__all__ = ['ARIANEApproach']

tas/setting.py

@@ -10,7 +10,7 @@ from lib.tas.benchmarking import AngleMap, AngleMapInducedMetric, \
 import sys
 
 # TODO: Import a subclass of `TASAutonomousApproach`.
-from tas.ariane_ import ARIANEApproach as Approach
+from tas.approaches import ARIANEApproach as Approach
 # from tas.approaches.dummies import RandomnessApproach as Approach
 # from tas.approaches.dummies import GridApproach as Approach