Particle

* Enhancements to ``Particle`` class:
- Particles in .dec decay files dealt with, see ``Particle.from_dec(...)`` method.
- Loading tables made nicer, with more documentation.
- Particle charge is an entry of CSV files again, so that user particles are better dealt with.
* Bug fix for corner cases of using the package for non-valid particles.
* Work on documentation.
* PyPI badge created from https://img.shields.io.

* Changes in API:
- Rename ``Particle.from_search/from_search_list`` to ``Particle.find/findall``.
- Rename ``Particle.fullname/name`` to ``Particle.name/pdg_name``.
- Rename ``Particle.bar`` to ``Particle.is_name_barred``.
- Rename ``Particle.latex`` to ``Particle.latex_name``.
* Neutrinos added to the 2018 data files.
* Better print-out of particle properties.
* Better handling of particle names in HTML and LaTeX.
* Better handling of ``Particle.empty()``.
* Test suite of ``particle`` and ``pdgid`` submodules improved and extended.
* Comprehensive package documentation (data files, ``particle`` and ``pdgid`` submodules).
* Added utility conversion function of particle names from LaTeX to HTML.
* Fixed LaTeX names of Delta(1232) baryons in ``data\pdgid_to_latex.csv`` file.
* Several bug fixes.
* Simpler usage of ``particle.particle.convert`` (non-public helper module).

* Particle search engine replaced with more intuitive and powerful version.
* Various improvements in the handling of particle names and literals.
* List of literals extended.
* More documentation in Particle class.
* More tests; table generation is now tested as well.
* Bug fixes in CSV data files and LaTeX naming updates.
* Added missing particles for 2018 data files.

* Bug fix in setup.py.
* CHANGELOG file added.

* `Particle` now has direct lifetime and ctau access.
* `Particle` and `PDGID` literals extended.
* Better documentation.
* Several bugs fixed in `Particle` and `PDGID`.
* The minimum version of dependencies are now more accurate.

The Scikit-HEP package `hepunits` is now a strict dependency.

Particle provides a pythonic interface to the Particle Data Group (PDG)
particle data tables and particle identification codes.