Also remove specific versions from numpy and h5py.

They catch the SystemExit and KeyboardInterrupt exceptions, which
usually nobody wants.

This is done by turning `correlation_axis` into a list.

A general description as well as instructions for installation and
building documentation are added.

The plot scripts are not very general, nice or userfriendly. Therefore
they are removed before publishing the repository.

The automatic generation of the documentation with GitLab CI stopped
working because installing h5py with pip caused errors. Using the
correct versions of python, numpy and h5py fixed this.