deprecate iterable of items (tuples) in most methods #1143
Description
meta, rename, reindex, set_axes, Session, stack and possibly others support list (iterables?) of tuples in addition to dicts.
while I am not super confident about #1142, I am pretty confident about this one. Ever since dicts preserve order, the list of tuples syntax has lost its main interest I think. It is longer to type and I don't think there is any significant performance difference either way.
For this issue, I would like to try deprecating it and see how it goes (do we use it internally, etc.).
The only downside I can see is the support for duplicated keys. For meta, rename, reindex, set_axes and Session, this is not a problem because we never supported (and will never support) duplicated keys in those contexts. For stack, we might need to keep that syntax specifically to allow duplicated labels (and possibly add explicit unit tests about them).