* Decays modelling:
- Updates to Mint related particle data files.
* Parsing of decay files (aka .dec files):
- Lark parser files added, for ``.dec`` decay files.
- ``DecFileParser`` class introduced, with documentation and test suite.
- Various ``.dec`` test decay files added.
* Visualisation of decay chains:
- ``DecayChainViewer`` class introduced, with documentation and test suite.
* Universal representation of decay chains:
- First "building block" classes ``DaughtersDict`` and ``DecayMode`` introduced,
with documentation and test suite.
* Package dependencies:
- Package made dependent on Scikit-HEP's ``Particle`` package.
- Redundant code removed.
* Continuous integration:
- CI with Azure pipelines introduced.
- CI with Travis and AppVeyor removed.
* Miscellaneous:
- Demo notebook added, with a launcher for Binder.
- Copyright statements added to repository files.
- General clean-up and minor bug fixes.