v0.2.0

Forked from the original pysigma-backend-stix repository: https://github.com/barvhaim/pySigma-backend-stix

The original repository has not been updated, so it is not compatible with new pySigma versions. This forked repo fixes this issue, and is compatible with pySigma = ">=0.9.5, <0.12.0" No other changes have been made to the repo besides the README and github workflows.