Issue #260: CURRENCY_META undocumented (blais/beancount)

[Martin Michlmayr]

New issue 260: CURRENCY_META undocumented
https://bitbucket.org/blais/beancount/issues/260/currency_meta-undocumented

Martin Michlmayr:

I don't know if this is a documentation issue or a bug but I cannot figure out how to use CURRENCY_META().

"help from" says it returns a dict. How do I query a dict in BLQ?

```
beancount> SELECT COMMODITY_META("GBP");
Traceback (most recent call last):
File "/usr/lib/python3.5/cmd.py", line 214, in onecmd
func = getattr(self, 'do_' + cmd)
AttributeError: 'BQLShell' object has no attribute 'do_SELECT'
...
File "/home/tbm/.local/lib/python3.5/site-packages/beancount/query/query_render.py", line 452, in get_renderers
for _, dtype in result_types]
File "/home/tbm/.local/lib/python3.5/site-packages/beancount/query/query_render.py", line 452, in <listcomp>
for _, dtype in result_types]
KeyError: <class 'dict'>
```

with

```
1970-01-01 commodity GBP
assets: "cash"

2018-02-17 * "Iceland" "Supermarket"
Expenses:Supermarket 2.00 GBP
Liabilities:Credit-Card -2.00 GBP
```