Draft: Merge version0.1 changes into dev

Working plotID package version 0.1.0 with basic functionality. It is ready for testing according. This can be done with the instructions from the README.

src/plotid/HDF5_externalLink.py

-"""Handling of hdf5 data files."""
-
-import h5py
-
-# Shows how to create an externalLink (symbolic) to a hdf5 File
-# Documentation available at:
-#    https://docs.h5py.org/en/stable/high/group.html#external-links
-myfile = h5py.File('./example.h5', 'w')
-myfile['ext link'] = h5py.ExternalLink("testdata_2.h5", "/")
-
-myfile.close()