add support for specifying arbitrary beancount options about ledger2beancount

[zacchiro]

the syntax of the needed configuration entry is not evident though, as options are key-value pairs, but the same key can appear multiple times, e.g.:

option "documents" "documents/2018"
option "documents" "documents/2017"
option "documents" "documents/2016"

[tbm]

Maybe we should just read an (optional) file and include that? Then you could define your headers somewhere and ledger2beancount adds it.

[zacchiro]

Yeah, that would be an option.
If we do that, though, we should drop the current support for the plugin configuration option, as it'd become redundant.

[tbm]

Agreed.

So should I implement that or do you have a better idea?

[zacchiro]

I'm fine with adding an option to specify a generic header file that should be inlined in the output to cope with current Beancount limitations.

[tbm]

Do you think we should remove operating_currencies from the config file since people can put that in the header or should I leave it there?

[zacchiro]

Yeah... good question. The generic mechanism is appealing for everything, I guess. But OTOH forcing people to create an extra file to be inlined for very commonly used options is awkward. Is my understanding that operating_currencies basically always needed correct? If so, I think it warrants special casing. If not, we can drop it.

[tbm]

I'm not sure it's needed for beancount itself but fava needs it. Anyway, since it's there already, let's leave it there.