Biip

- This release adds extended support for UPC, especially the UPC-E format. (Fixes: 77, PR: 78)

- Parse 12-digit UPC-A. This is the same as GTIN-12, so it is strictly already supported.
- Parse 6-digit UPC-E, with implicit number system 0 and no check digit.
- Parse 7-digit UPC-E, with an explicit number system and no check digit.
- Parse 8-digit UPC-E, with an explicit number system and a check digit.
- Expand UPC-E to UPC-A.
- Suppress UPC-A to UPC-E, for the values where it is supported.

- The top-level parser has been slightly changed so that the first successful parse result from each parser is the result that is kept. E.g. if parsing a number that is both a valid GTIN-8 and UPC-E, the `gtin` field will contain the result of parsing it as GTIN-8, not the result of expanding the UPC-E result to a UPC-A (which is the same as GTIN-12) set in the `gtin` field.

If you're using Biip, please add yourself to the new [list of users](https://github.com/jodal/biip/wiki/Users)!

The library has now been in production use for more than a half year. It has parsed millions of barcodes during this time, only uncovering a single bug that has long been fixed. As all planned features have been implemented and the library seems to be solid, it's time for a 1.0 release, marking the library as stable and production-ready.

If you're using Biip, please add yourself to the new [list of users](https://github.com/jodal/biip/wiki/Users)!

Changes

- Update the bundled GS1 Application Identifier definitions.

- Support specifying `rcn_region` as a string, e.g. `"no"`, instead of `RcnRegion.NORWAY`. The type annotations still expect a `RcnRegion` instance, which is the recommended way to use the API. By supporting strings instead of `RcnRegion` instances, the API is a bit easier to use interactively in a REPL.

- Add `py.typed` marker file, as specified in PEP561, as Biip is fully typed.

- Fix documentation build.

- Fix `__all__` export of `biip.DEFAULT_SEPARATOR_CHARS`.

- Add Python 3.6 support, using the `dataclasses` backport for Python 3.6.

- Add Python 3.9 to the test matrix.

- Bugfix: Add zero in front of GTIN-12 before extracting GS1 Prefix. GTIN-12s start with U.P.C. Company Prefixes, which have to be padded with a zero in front to convert them to valid GS1 Company Prefixes.

- Change the error message in the top-level parser's `ParseError` to include the name of data type we failed to parse.