Instead of converting all journal amounts to value early on, we now
convert just the report amounts to value, before rendering.
This was basically how it originally worked (for the balance command),
but now it's built in to the four basic reports used by print,
register, balance and their variants - Entries, Postings, Balance,
MultiBalance - each of which now has its own xxValue helper.
This should mostly fix -V's performance when there are many
transactions and prices (the price lookups could still be optimised),
and allow more flexibility for report-specific value calculations.
+------------------------------------------++-----------------+-------------------+--------------------------+
| || hledger.999.pre | hledger.999.1sort | hledger.999.after-report |
+==========================================++=================+===================+==========================+
| -f examples/1000x1000x10.journal bal -V || 1.08 | 0.96 | 0.76 |
| -f examples/2000x1000x10.journal bal -V || 1.65 | 1.05 | 0.73 |
| -f examples/3000x1000x10.journal bal -V || 2.43 | 1.58 | 0.84 |
| -f examples/4000x1000x10.journal bal -V || 4.39 | 1.96 | 0.93 |
| -f examples/5000x1000x10.journal bal -V || 7.75 | 2.99 | 1.07 |
| -f examples/6000x1000x10.journal bal -V || 11.21 | 3.72 | 1.16 |
| -f examples/7000x1000x10.journal bal -V || 16.91 | 4.72 | 1.19 |
| -f examples/8000x1000x10.journal bal -V || 27.10 | 9.83 | 1.40 |
| -f examples/9000x1000x10.journal bal -V || 39.73 | 15.00 | 1.51 |
| -f examples/10000x1000x10.journal bal -V || 50.72 | 25.61 | 2.15 |
+------------------------------------------++-----------------+-------------------+--------------------------+
There's one new limitation, not yet resolved: -V once again can pick a
valuation date in the future, if no report end date is specified and
the journal has future-dated transactions. We prefer to avoid that,
but reports currently are pure and don't have access to today's date.
Since market price amounts didn't contribute to the canonical commodity
styles, they were being reset to the null style. And this propagated to
the reported amounts when -V was in effect, causing much confusion.
Now, market prices contribute to canonicalisation and the expected
styles are preserved even with -V.
cf https://github.com/simonmichael/hledger/issues/131#issuecomment-133545140
