Rename data_capture

Currently there is one statistic that returns the data capture and it is named data_capture. However each statistic in the package has an argument called data_capture which is used to give the minimum number of available data in an interval so that a value is returned for that interval.

The function data_capture should probably be renamed to avoid a function signature like this:

def data_capture(df, dfref, mtype, metadata, seasons, data_capture)