ellipsoid self modification about dynesty

[joshspeagle]

Started working on this, and then realized that while this might be fine for a single Ellipsoid, the number of ellipsoids generated by bounding_ellipsoids (and _bounding_ellipsoids) is not fixed by design. This poses a problem for allowing internal updates in MultiEllipsoid, since we'll need to initialize new Ellipsoid objects anyways. While we could get around this with extra bookkeeping (adding ellipsoids to a list, updating them as we go, making them as "dead" when we want to ignore them, and appending new ones as we need them), I don't think this translates cleanly into self-modification.

I think I can still add in a bound method for the two classes though to allow them to be instantiated once and then be modified by users.

[bd-j]

ok, not worth much effort if it's not easy as there's no actual new functionality.