FinanceFerret/version 2

transaction engine
This is the core of FinanceFerret. It handles:
 * recording transactions
 * up to three entries per transaction:
 * source account
 * destination account
 * equity account -- is this necessary? need to straighten out how equity works.
 * calculating balances in different ways:
 * different sortings (checkbook, bank...)
 * arbitrary lists of transactions (e.g. for budgeting)

category manager

 * assigning categories to transactions or parts of transactions
 * building lists of transactions that fall within a given category

account manager

 * who owns what accounts
 * who has permissions for each account, and which permissions (read? write? other?)
 * units (type of currency)