v2.1.0

Major changes:

• Popper now finds minimal unsatisfiable cores of totally incomplete programs, as described in the paper: Learning Logic Programs by Finding Minimal Unsatisfiable Cores, A. Cropper and C. Hocquette, AAAI 2023, which should reduce learning times a lot

Minor changes:

• Faster way to test single rule programs
• Experimental feature to discover constraints from the BK before searching as described in the paper: Learning Logic Programs By Discovering Where Not to Search, A. Cropper and C. Hocquette, AAAI 2023. Enable this feature with the --bkcons flag