Updating invoice_items schema. Changing price, rental_rate, and discount fields to DECIMAL types instead of DOUBLE. Also, updating INT fields to INT(11) as opposed to INT(20) and setting them all to UNSIGNED. Also deleted the date_created field as it is redundant given that invoice_items are contained on an invoice, which is already storing that information. Also updated date_out, date_due, and date_returned fields to use DATETIME type instead of INT.
See previous commit notes for information about this change set.