Release 0.4.3

[mantkiew]

• added language feature with backend compatibility table
• added support for nested abstract clafers to Choco generator
• added checks for loops in inheritance hierarchy, issue 77
• fixed an issue with inheritance from a nested abstract clafer which itself has a superclafer, issue 78
• added min/max to Alloy generator, issue 79
• removed the unused and outdated python mode -m python
• fixed handling paths containing spaces in validation