Income, liability and equity balances, which until now we have
always displayed as negative numbers, are now shown as normally positive
by these reports.
Negative numbers now indicate a contra-balance (eg an overdrawn
checking account), a net loss, a negative net worth, etc.
This makes these reports more like conventional financial statements,
and easier to read and share with normal people.
* Add an option to use unicode in balance tables
fixes#522
* Add a test for unicode tables
* Document --pretty-tables
* Support --pretty-tables in BalanceView