books: All tools use books.Loader.dispatch() and LoadResult.

This is significant code deduplication, as seen in the diffstat.

plugin: Skip enum value checks with a flag+FIXME.

We've long supported skipping documentation checks by flagging the
transaction. We haven't done the same for enumerated metadata because we
need it less often, and bad values tend to do more damage to reports.

However, occasionally when something very off-process happens, we do need it
as a matter of expediency. So support it.

In order to skip validation of these fields, the plugin requires that the
value start with the string "FIXME". This helps ensure that reports have a
consistent way to detect and warn about unfilled values in flagged
transactions.

plugin: Add TransactionDate hook. RT#10566

This prevents mistakes where a transaction is entered in the wrong file for
its date (which in turns causes errors in reports).

ledger: --account accepts a classification.

This makes it easier for users to specify a group of accounts.

data: Add Account.is_account and Account.load_options_map.

These work in concert to distinguish account names from other
colon-separated strings.

cliutil: Add make_entry_point() function.

This provides better logging setup, reduces the amount of boilerplate in
main, and replaces is_main_script().

reports: Balance is initialized with just amounts.

This works fine with how we're currently using it, makes transformation
methods easier to implement, and avoids potential bugs where a balance is
initialized with a bad mapping.

books.Loader: New loading strategy based on load_file. RT#11034.

Building a string and loading it means Beancount can never cache any
load. It only caches top-level file loads because options in the
top-level file can change the semantics of included entries.

Instead use load_file as much as possible, and filter entries as
needed.

books.Loader: New loading strategy.

The old loading strategy didn't load options, which yielded some
spurious errors. It also created awkward duplication of plugin
information in the code as well as the books.

Implement a new loading strategy that works by reading one of the
"main files" under the books/ subdirectory and includes entries
for additional FYs beyond that.

This is still not ideal in a lot of ways. In particular, Beancount can't
cache any results, causing any load to be slower than it theoretically could
be. I expect more commits to follow. But some of them might require
restructuring the books, and that should happen separately.

reports.accrual: Begin reporting.

This module basically reimplements the old payment-report+income-report,
in a single tool (after setting aside some of the checks that have moved
to the plugin). The aging report can be implemented here too when we need
that.

tests: Test where Transactions are real NamedTuples.

This makes methods like _replace available in real code, and caught the
bug where we can't use @functools.lru_cache with Transaction arguments,
because they're unhashable due to their mutable members.

data: Fix Amount.__new__.

See the comments for background and rationale.

data: Add Metadata class.

As I start writing more link-checking hooks, I want a common place to
write link-parsing code. This new class will be that place.

rtutil: Start module.

For now, this is basically the Python version of
ledger-tag-convert.plx. It knows how to create RT web links from
ticket and attachment IDs. It confirms that those objects actually
exist too. It may grow to encompass other functionality in the
future.

config: Add Config.rt_credentials method.

This loads settings from the same environment variables and ~/.rtrc
file as the rt CLI.

Note that it does *not* support RTCONFIG and the config file
searching, because right now that seems like more work for more
trouble to me.

testutil: Improve check_post_meta error reporting.

This version makes it easier to get diffs between the expected
and actual metadata.

tests: Add check_post_meta.

This makes it simple to conveniently check all posting metadata in tests.

plugin.core: _meta_set properly handles when post.meta is None.

post is a NamedTuple, so attribute assignment is not allowed.
Instead we have to construct a whole new Posting.

expenseAllocation: Date-limit the transactions we work on.

This prevents the plugin from giving meaning to postings that
might not really be there.

expenseAllocation: Start checker.

This is the simplest version of a common validation we're going to do:
make sure that a particular piece of metadata has one of a set of
values.

This checker needs some bounds checking but I wanted to err on the
side of committing this early because it introduces so much base
infrastructure.