Add __version__ attribute to OMPython

[adeas31]

Description

OMPython should define a __version__ attribute so that its installed version can be easily queried and reported programmatically.

Expected behavior

Users should be able to do:

import OMPython

print(OMPython.__version__)

and get the installed OMPython version.

Motivation

This would make it easier for users and applications to report the OMPython version when troubleshooting, collecting environment information, or generating bug reports.

[adeas31]

@cbu-hw

[adeas31]

Fixed with #480