I found that this project has extensive capabilities for accessing object attributes and pretty-printing values of many different types, but it was only being used for printing locals in a stack frame and for some thread introspection. The potential for other uses is immense.

This PR adds a new command called objects, which allows introspection into live objects of an interpreter instance by walking the GC. It's supported for both, active processes and core dumps. All Python versions with active support are covered. Prior to 3.9, GC structures looked a bit different.

Use cases:

• Debugging: What instances of a specific type are there and what values do specific attributes in them have?
• Forensics: Access runtime values in a Python process dump (possibly taken from a full system memory dump), e.g., to inspect malware.

A potential future extension could be to take an object address and print its entire attribute dict.