Adapted the 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
+calculate_trend - calculate the trend using the requested method
 """
 
 import statsmodels.formula.api as smf
 
 
-def calculate_quantile_regression(quantiles, data):
-    """Calculate the quantile regression.
+def calculate_trend(method, data, formula="value ~ datetime", quantiles=None):
+    """Calculate the trend using the requested method.
 
     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.
+    trend analysis.
 
-    :param quantiles: a single quantile or a list of quantiles to
-                      calculate, these must be between 0 and 1
+    :param method: either ``"OLS"`` or ``"quant"``
     :param data: data containing a list of date time values and
                  associated parameter values on which to calculate the
-                 quantile regression
+                 trend
+    :param formula: the formula specifying the model
+    :param quantiles: a single quantile or a list of quantiles to
+                      calculate, these must be between 0 and 1; only
+                      needed when ``method="quant"``
     """