Hledger.Data.Balancing.
Both Hledger.Data.Transaction and Hledger.Data.Journal are massive
module with many things in them. Placing the balancing functions, which
are conceptually related, into a separate module helps keep things more
modular.
It also reduces the risk of import cycles, as right now balancing
functions cannot depend on any functions defined outside of
Hledger.Data.Transaction or Hledger.Data.Journal, respectively, if those
modules require basic transaction or journal functions.
The forecast period begins on:
- the start date supplied to the `--forecast` argument, if present
- otherwise, the later of
- the report start date if specified with -b/-p/date:
- the day after the latest normal (non-periodic) transaction in the journal, if any
- otherwise today.
It ends on:
- the end date supplied to the `--forecast` argument, if present
- otherwise the report end date if specified with -e/-p/date:
- otherwise 180 days (6 months) from today.
Note that the previous behaviour did not quite match the documentation,
so this also acts as a bug fix for #1665.
