[Request] Implement pretty printing support in Jupyter notebook

[shunghsiyu]

Jupyter notebook and drgn seems to be a really great combination, it'd would be nice to see pretty printing of drgn object in Jupyter notebook implemented for a even better synergy (similar to what's being done in interactive mode).

In theory implementing _repr_pretty() is all that's needed, something like what stackoverflow suggests, but done with C inside libdrgn/python/object.c.

    def _repr_pretty_(self, p, cycle):
       p.text(str(self) if not cycle else '...')

[osandov]

I'm closing this one now since your pretty printing support was previously merged. #318 will track further integration.