Use latest SBCK, eofs

[Zeitsperre]

Pull Request Checklist:

• This PR addresses an already opened issue (for bug fixes / features)
  • This PR fixes #xyz
• Tests for the changes have been added (for bug fixes / features)
  • (If applicable) Documentation has been added / updated (for bug fixes / features)
• CHANGES.rst has been updated (with summary of main changes)
  • Link to issue (:issue:number) and pull request (:pull:number) has been added

What kind of change does this PR introduce?

• Sets sbck git-based install to use their master branch at SBCK-python
• Adds sbck to conda environment.yml (via git+https install)
• Adds sbck and eofs as tox modifier flags for easier testing
• Adds step for installing Eigen3 core library to CI build for testing sbck tox builds.
• Updates installation documentation for clarity.

Does this PR introduce a breaking change?

No. The package dependencies on typical or upstream installation are unaffected.

Other information:

yrobink/SBCK-python#1

Related? #1204

[Zeitsperre]

Marking approved to trigger upstream tests only.

[coxipi]

Everything seems good. Not sure what #egg=blabla in the links is supposed to mean though

[Zeitsperre]

Not sure what #egg=blabla in the links is supposed to mean though

egg= is the original method for specifying the name of a dependency when coming from a VCS system (like git). I just learned today that the newer approach is to use <package_name> @. Will update to see if that works for us (it looks nicer as well).

More information: https://pip.pypa.io/en/latest/topics/vcs-support/?highlight=egg#git

[aulemahal]

Agreed for the changes concerning SBCK, but I'm not sure eofs deserves this.

[coveralls]

Changes Unknown when pulling efe163d on use_SBCK_master into ** on master**.