Particle

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.

* Changes in API:
- ``GeantID`` class renamed to ``Geant3ID``.
* Data CSV files:
- Version 3 (and 2) of package data files,
which contain new entries and fixes for certain information in 2008 PDG extended data file.
- File ``data/pdgid_to_geantid.csv`` renamed to ``data/pdgid_to_geant3id.csv``.
- 2016 and 2017 PDG data files ``mass_width_2016.mcd`` and ``mass_width_2017.mcd`` removed.
* Tests:
- Tests for ``converters`` submodule added.
- Tests for ``Geant3ID`` extended.
* Miscellaneous:
- Package files formatted with ``Black`` package.

* ``Particle`` class:
- Isospin property returns a float.
- New property ``is_unflavoured_meson``.
- More tests for P and C quantum numbers.
* ``PDGID`` class:
- Non-robust P and C properties removed.
* Data CSV files:
- Versioning introduced, see comment on first line of files.
- File ``data/pdgid_to_evtgenname.csv`` extended with extra information.
- More documentation.
* MC particle identification code converters:
- Core ``BiMap`` class simplified.

* Enhancements to ``Particle`` class:
- Dummy/unknown particle width and lifetime errors stored as ``None``.
- More particle name and ``PDGID`` literals for b-baryons.
- Fix for the ``D(s2)*(2573)`` LaTeX name.
- ``InvalidParticle`` made available at top-level import.
* Changes in API:
- ``Particle.from_dec...()`` renamed to ``Particle.from_evtgen_name(...)``.
* MC particle identification code converters:
- Introduced directional maps ``PDG2EvtGenNameMap`` and ``EvtGen2PDGNameMap`` between PDG and EvtGen names.
- Conversions master file ``data/conversions.csv`` added.
- Content of converters CSV files are now ordered.
* Documentation:
- README updated with new package functionality.
* Support for Python 3.4 removed and support for Python 3.8 added.