Use metadata symbols, conversion func if needed

Tried multiple invocations of the recursive symbols_to_strings but
haven't gotten it to work. For now I'll embrace symbols, although for
more standard YAML they may need to be eliminated eventually.
YAML transcription draft functionality

It works, a couple of things:

 - Any other metadata fields?
 - :Morphology is a key in @annotations, which is not the common %mor
 tag. I think eventually I'll just transition to all of the shortened
 tags exclusively in keeping with the "transcription" format