Package reorganisation and conversion / filter separation

• Reorganise potentially reusable elements under a pm superpackage. This breaks back compatibility, and we are under version 1, so issued a minor version. Impacted:
• • loggen log generation
• • ssnap State Snap Miner
• • pmmodels Petri net and other model utilities
• Separate conversion and filtering in cgedq/conv.py, making reuse easier.
• • Add cgedq/regionmine.py, work in progress.