Pyhepmc

What's Changed
* Support reading/writing compressed files by HDembinski in https://github.com/scikit-hep/pyhepmc/pull/44

**Full Changelog**: https://github.com/scikit-hep/pyhepmc/compare/v2.6.1...v2.7.0

What's Changed
* Fix license issues by HDembinski in https://github.com/scikit-hep/pyhepmc/pull/38
* Increase coverage by HDembinski in https://github.com/scikit-hep/pyhepmc/pull/41


**Full Changelog**: https://github.com/scikit-hep/pyhepmc/compare/v2.6.0...v2.6.1

What's Changed
* Particles can be assigned as attributes by HDembinski in https://github.com/scikit-hep/pyhepmc/pull/39
* Attributes after deserialisation are now represented by the UnparsedAttribute class, which allows conversion into concrete attribute types by HDembinski in https://github.com/scikit-hep/pyhepmc/pull/39

**Full Changelog**: https://github.com/scikit-hep/pyhepmc/compare/v2.5.1...v2.6.0