I saw some terrible things in the indexing code. It's practically unreadabele. I fear
that by plugging it in there, we'll remain stuck where we only get a soul brave enough
to improve things once every 18 months. or you have to do it.

_get_loc_level returns a slice right? If I'm not wrong, it returns a slice relative to the
whole array, rather then per level, which I find easier to grok code wise,
and aides the lazy generation later on. Not that we have a lazy consumer to plug it into.