ENH: add hdf5 io and AverageRFR IO capacities

as the name explains: put TFR objects in a fiff. Tests pass on my box.

cc @agramfort
cc @virvw
Why is this necessary? I'd rather improve the read/write capability than have to restrict it. If you do this because it adds a bunch of unnecessary info, I'd rather have a function like `smaller_info = reduce_info(info)` to do this work.