Added a template for the public interface of the trends subpackage.

toarstats/trends/interface.py

+"""This module contains the public interface for the trends subpackage.
+
+This module contains the following function:
+calculate_quantile_regression - calculate the quantile regression
+"""
+
+import statsmodels.formula.api as smf
+
+
+def calculate_quantile_regression(quantiles, data):
+    """Calculate the quantile regression.
+
+    This function is the public interface for the ``trends`` subpackage.
+    It takes all the user inputs and returns the result of the requested
+    quantile regression.
+
+    :param quantiles: a single quantile or a list of quantiles to
+                      calculate, these must be between 0 and 1
+    :param data: data containing a list of date time values and
+                 associated parameter values on which to calculate the
+                 quantile regression
+    """