Merge branch 'niklas_issue005_refac_refactor-and-expand-testing' into 'develop'

.gitignore

requirements.txt

tests/conftest.py

tests/test_metrics/.gitignore

tests/test_metrics/conftest.py

.../test_metrics/create_sample_data_and_reference_results.py

tests/test_metrics/test_input_checks.py

tests/test_metrics/test_interface.py

tests/test_metrics/test_stats.py

tests/test_metrics/test_stats_utils.py

tests/test_metrics/test_toarstats.py

tests/test_metrics/time_series.csv

tests/test_trends/__init__.py

tests/test_trends/conftest.py

tests/test_trends/test_interface.py

tests/test_trends/test_ols.py

tests/test_trends/test_quant_reg.py

tests/test_trends/test_utils.py

toarstats/metrics/input_checks.py

toarstats/metrics/ozone_metrics.py