Allow to include vertex info via format option system

[HDembinski]

The Root writer does not write the vertex info by default to save disk space. It was foreseen to optionally save the vertex info, but a configuration option was missing.

I now added a configuration system for the output format. You can now provide options to the format via colon, e.g. format:option1:option2[...]. Currently, there are two formats which accept options.

• hepmc accepts gz, e.g. you can pass hepmc and hepmc:gz
• root accepts vertex, e.g. you can pass root and root:vertex

[HDembinski]

The Windows failure is not related to this change, but because we hit the download limit, also see #132

[afedynitch]

Neat. Windows test failed because of download limit, so feel free to merge.