Map for iterating over extracted EXIF fields

[evanoberholster]

Is there a way to get all the extracted EXIF fields? Like a map I can iterate over?

It's OK if these fields don't have any special interpreation: just a key-value store of whatever fields were discovered. This would be easier for me to work with than a huge struct with hard-coded fields. (I think some struct fields are OK, especially if they are common or need interpretation to be useful -- but I'd still like a map of everything that was parsed anyway.)

Originally posted by @mholt in #48 (comment)

[mholt]

I might add too, since I see this package supports more than just EXIF (which is awesome!) that it'd be useful to iterate over any/all extracted metadata even if it's not EXIF. Doesn't have to be in the same structure, but some way to iterate EXIF, a way to iterate XMP, etc. Maybe it's the same way, that's cool too.

Thanks for your excellent work on this lib 💯