Pyproject.toml transition

Move building the package from setup.cfg to pyproject.toml. How it looks on PyPI can be viewed here:
https://test.pypi.org/project/plotID/
It remains to be discussed who we should mention as author in the init.py which is used for the author in the documentation. But I actually like that the author is the institute in the documentation but is referenced as last in the metadata...

Closes #89 (closed)

plotid/__init__.py

@@ -10,5 +10,5 @@ research data, the plot is based on. Additionally, the script that created the
 plot will also be copied to the directory.
 """
 
-__version__ = '0.2.1'
+__version__ = '0.2.2'
 __author__ = 'Institut Fluidsystemtechnik within nfdi4ing at TU Darmstadt'