Move main() code into test_ file

[wdoekes]

Moving the main() code to a test_pysigset.py file makes sense:

• better BCH points
• less code loaded into memory which we're not using

Don't forget to update pysigset version and pushing to pypi when fixing stuff.

[wdoekes]

This would also create an initial test. And make BCH happy for that reason. Double profit.