implement object[Integer...]

Maybe make `object[i,j,...]` in Julia sugar for `get(object, (i,j,...))`, equivalent to `object[i,j,...]` in Python, for the common case of integer indexing (e.g. #149).

I would prefer to just make `object[...]` equivalent to `object[...]` in Python regardless of the index type, but then I wouldn't have a good syntax for Python's `object.attribute` (until some future Nirvana when dot overloading arrives in Julia).