Map a function to a list of keywords

        Parameters
        ----------
        keywords : iterable of str
            sequence of strings which should trigger the given function
        context : Context
            A Context object created using desired function
        rule : tuple
            A tuple of integers, which act as relative indices using which data
            is extracted to be passed to the function passed via context.

def add_task(self, keywords, context, rule):
        """Map a function to a list of keywords

        Parameters
        ----------
        keywords : iterable of str
            sequence of strings which should trigger the given function
        context : Context
            A Context object created using desired function
        rule : tuple
            A tuple of integers, which act as relative indices using which data
            is extracted to be passed to the function passed via context.
        """
        for keyword in keywords:
            self._tasks[keyword] = {'context': context, 'rule': rule}