Added barcode field

[SimonHova]

I added the barcode field to clear issue #26.

[sampsyo]

Looks great so far! We'll need to do a couple of things:

• Update the tests to include the new field.
• Double-check the new tag mappings against existing software, especially the Picard tag mappings.

[SimonHova]

The tag mappings look pretty straightforward, with the exception of the iTunes. But, I matched with another field, and it looks good now. Tell me what you think.

[sampsyo]

Looks pretty good to me, and it seems to match the Picard mappings! Can you elaborate on what was less straightforward about the iTunes (MPEG-4) tag?

[SimonHova]

Sure. All the other tags had the name barcode, but the iTunes one had six dashes instead. I'm presuming that means that iTunes doesn't support the field, but I copied the format which had an identical format from another field, so I'm confident that it's correct.

[sampsyo]

Just checking, do you mean four dashes, as in ----:com.apple.iTunes:BARCODE? That is indeed what Picard seems to use, which is a good indication that it's also what other software uses. (It's worth mentioning that compatibility with other software is the paramount concern.)

[SimonHova]

That is absolutely correct, I copied the format from another field that had a similar notation in the table.

[sampsyo]

Perfect; thanks!! Merged. ✨