Credit Note Line Item Tax Rate Stored as Integer

[armordog]

I'm synchronizing to RDS.

In the invoices__line_item_taxes table, the tax_rate column is stored as a bigint.

This means that tax rates are truncated to the nearest whole percent (eg: Quebec QST is truncated from 9.975 to 9).

[armordog]

PR here: #80

Note: I'm not sure what happens to existing tables when you change the type of a column.