Creates a dictionary representing the state of this position.
        Returns a dict object of the form:

def to_dict(self):
        """
        Creates a dictionary representing the state of this position.
        Returns a dict object of the form:
        """
        return {
            'sid': self.asset,
            'amount': self.amount,
            'cost_basis': self.cost_basis,
            'last_sale_price': self.last_sale_price
        }