Iterator::size_hint() #7
Description
Add an implementation for Iterator::size_hint() to the Iterators.
This should be fairly straight forward. The upper bound will be the length of the internal slice or vector, and the lower bound will be zero or one, depending on if iteration is completed yet.
Using autocfg, we may be able to implement TrustedLen for these iterators as well. For this to happen, channel probing will need to land on the autocfg side first.