ENH: GroupBy.get_group should accept lists with multiple grouping keys
In 1.3.4, if you call the get_group function and pass it a list of keys it will raise a value error

_ValueError: must supply a tuple to get_group with multiple grouping keys_

but it is not very clear why it must be a tuple as opposed to any iterable. I prefer to use lists, that way I can use square brackets in the function call and to me it looks better than adding more parenthesis. Thanks!