Allow for embedding of certain configuration values directly within a journal

[micahellison]

Feature Request

I was discussing time stamps with @wren today and thinking how some configuration values have less to do with the behavior of the overall application or where to find a journal but instead with how the journal itself is formatted. It can be dangerous, even, to change these values, as it affects how the journal is written and read. This is extra problematic for users that sync journal files across systems: they better be syncing their configs too, or at least manually ensuring that the config values are the same. And for users interested in long-term data preservation, it's unlikely that they are backing up their configurations as regularly as their journals, if they are at all.

A way around these problems could be to allow for some sort of header or footer in the journal file itself where a user could store these values. I'm specifically thinking of the timeformat field but default_hour, default_minute, linewrap, tagsymbols, and maybe even version could be useful. Some fields, like encrypt and journal, couldn't possibly be retrieved here, however.

Order of precedence would be important too. Right now, we have two levels of configuration: application-wide, and journal-specific. Journal-specific configuration overrides application-wide configuration. This enhancement would add a third level that would override the other two. Some sort of configuration display tool might be useful to make it clear which setting jrnl is actually using for a particular journal.