Versioneer

This MR enables Versioneer to have a consistent way for pystencils to get a version string

pystencils_tests/test_version_string.py

-import pystencils as ps
-from pathlib import Path
-
-def test_version_string():
-    file_path = Path(__file__).parent
-    release_version = file_path.parent.absolute() / 'RELEASE-VERSION'
-    if release_version.exists ():
-        with open(release_version, "r") as f:
-            version = f.read()
-        assert ps.__version__ == version
-    else:
-        assert ps.__version__ == "development"