Feature Request: categorical.reset_order
I was thinking about trying to add a `to_unordered` method, then I thought maybe a `reset_order` (or `reorder`?) with an optional `drop` keyword à la `reset_index` makes more sense. I didn't see if this was possible yet, so this is also a question. Is this possible via some other syntactic sugar? I might see if I can hack this together at some point unless someone beats me to it. My motivation for this is that I'm getting all ordered or unordered factors using `read_stata`. This could be "fixed" there by taking a list in addition to the boolean convert to ordered or whatever, but I think a method like this would be generally useful, plus I never peak at data before reading it. 
