Inspect objects in existing Python REPL.

Once you have started a Python process with `run-python' and defined a variable, you can
inspect an object by putting your cursor on it and running `pyinspect-inspect-at-point'.
You'll get into an inspection buffer dedicated to this object. You can navigate in and out of
each field with `i' and `u', and move between same-level fields with `n' and `p'.
Once you're done, hit `q' to close all the pyinspect buffers.