Improve the version file information

This adds the version information (and the git tag), e.g.

>>> import pyfstat
>>> pyfstat.__version__
'1.3: (CLEAN) 4fdfc02 2020-01-22 08:40:17 +1100'

pyfstat/__init__.py

@@ -26,3 +26,7 @@ from .grid_based_searches import (
     SliceGridSearch,
     TransientGridSearch,
 )
+
+
+from .helper_functions import get_version_information
+__version__ = get_version_information()