* Changed behavior of `readJournalFiles` to be identical to `readJournalFile` for singleton lists
* Balance Assertions have to be simple Amounts
* Add 'isAssignment' and 'assignmentPostings' to Hledger.Data.Posting and Transaction
* Implemented 'balanceTransactionUpdate', a more general version of 'balanceTransaction' that takes an update function
* Fixed test cases.
* Implemented balance assignment ("resetting a balance")
* Add assertions to show function
* updated the comments
* numbering is not needed in journalCheckBalanceAssertions
* remove prices before balance checks
* rename functions
Using "hledgerdev" was a hack to help ensure that tests used a fresh
developer build by default. Now they specify "hledger" again, which fits
better with stack. It's up to the tester to make sure the desired
executable is first in PATH or specified with -w. (Note a couple of
tests currently don't obey -w and will always run "hledger", see addons.test).
This change means you can make assertions on a multi-commodity account
balance (asserting one commodity at a time). On the flip side, you can
no longer assert the complete balance of an account (new unexpected
commodities will not be detected.) We might restore that ability later,
using the == syntax.
