Particle

- Data files:
- Added the 2020 PDG data table .mcd file, now default.
- Version 6 of package CSV data files:
- Since PDG 2020 information now the default.
- Bug fix in parity of antibaryons.
- Documentation:
- README updated and expanded with info on custom data loading.
- Miscellaneous:
- ZipApp fix for releasing from web interface.

- `Particle` class:
- Several improvements, in particular to better deal with nuclei
and diquarks.
- Speed of table loading improved.
- Particle enums extended for diquarks.
- Make particle literals available from top-level import.
- Print-outs made more consistent for missing and non-relevant
particle properties.
- New tests added, some static type checking.
- `PDGID` class:
- PDG ID functions extended to correctly and consistently deal
with nuclei.
- Functions now accept any SupportsInt, including Particle objects.
- Data CSV files:
- Version 5 of package data files:
- Diquarks added.
- Information in nuclei added! List and masses taken from
package `periodictable` version 1.5.2.
- A couple of PDG ID numbers corrected (they had evolved in
time).
- Converter script adapted to add to the produced data files
particles not in the PDG data table, such as diquarks.
- Redesigned packaging system, GHA deployment.
- Miscellaneous:
- Files `*requirements.txt` removed from package - use
`pip install .[dev]` instead
- Warning from `collections.abc` fixed, keeping compatibility with
Python 2.
- Deprecation warning in `attr.s` fixed, requirement on minimal
version of `attr` added.
- Version tags now follow standard `v..` format.
- Some Python warnings fixed, warnings enabled on testing
- Some initial work on static type hints.
- ZipApp fixes, simplifications and size reduction; ZipApp now
requires `python3` to be available

* ``Particle`` class:
- Deal with particles with no mass info.
- Make ``Particle.dump_table()`` work better in notebooks.

Particle`` class:
- Documentation added to various methods.
- Minor fix to class method ``from_evtgen_name(...)``.

* ``Particle`` class:
- Robust handling of missing mass info.
* Data CSV files:
- Version 4 of package data files,
with more particles added (mostly badly-known particles relevant for MC).
- Version header now also present in the ``particleXXXX.csv`` files.

* Fix of lifetimes/widths (unknown) for corner cases.
* Documentation updates.