This allows for value expressions to be used which reference the
incoming posting, for example:
= Income:Clients:
(Liabilities:Taxes:VAT1) (floor(amount) * 1)
(Liabilities:Taxes:VAT2) 0.19
2009/07/27 * Invoice
Assets:Bank:Checking $1,190.45
Income:Clients:ACME_Inc
The automated posting for VAT1 will use the floored amount multiplied by
a factor, while the posting for VAT2 multiples the whole amount as
before.
