HepMC-3.0.0-bp150.2.5

- Reapply shared library guidelines.
- Add sover.diff to force shlib versioning.
- Slightly trim description for length.

- Update to version 3.0.0:
  + See list of changes from:
    https://gitlab.cern.ch/hepmc/HepMC3/blob/3.0.0/ChangeLog.
- Drop shared library subpackage; there is no numbered shared lib
  any more. Package everything into the devel package.
- Use cmake macros for build and install.
- Drop unused cmake options.
- Build and install doxygen documentation.
- Manually install examples to docdir, running fdupes to weed out
  duplicated files.
- Update URL and Source URL for new upstream links.
- Updated file-list.

- Initial version