Bibtextools

Added
- Added function to abbreviate journal names based on the ISO4 standard using
the `pyiso4` implementation as part of the `modernize` command.

Changed
- Update packaging structure and metadata from old `setup.py` to
`pyproject.toml`
- Change minimum Python version requirement to 3.8 due to the pyiso4 dependency

Added
- A completely refactored command line interface using the `click` library is
added. This will replace the current CLI in a future version.

Fixed
- Fixed a bug in getting author names when shielded umlauts were already
present.

Added
- It is now possible to change the sorting of the entries when writing to a
file
- Added the `shield_title` argument for modernizing the title field, which
allows adding/removing curly brackets around the title field.
The argument can be used by setting the `--shield_title` flag in the
`modernize` command.

Changed
- The fields `keyword` and `keywords` do not get removed by default
- Surrounding curly brackets in the title field are removed by default. Use the
`--shield_title` argument to avoid this.

Fixed
- Already converted unicode symbols are not touched when cleaning unicode
characters.
- Improve author name cleaning in `modernize` subcommand. Names that are
shielded by `{}` are now split into first and last names respecting the
grouping.

Fixed
- Acronyms that are already shielded by `{}` will not be shielded again when
modernizing a bib file.

Added
- Added subcommand functionality. Available subcommands are `clean`, `combine`,
and `modernize`.
- Added `clean` functionality, that e.g., allows renaming duplicate IDs.
- Added `combine` functionality that allows combining multiple bib files into a
single one.
- The minimum required version of Python is 3.7.