ptr: inline the Clone implementation
kinds: update documentation
update the iterator tutorial
tuple: remove obsolete ExtendedTupleOps

replaced by iterators (generic composable `map` and `zip` adaptors)
vec: rm obsolete zip and zip_slice

These are obsoleted by the generic iterator `zip` adaptor. Unlike
these, it does not clone the elements or allocate a new vector by
default.
iterator: cleanup
vec: rm redundant is_empty implementations
auto merge of #8503 : thestinger/rust/iterator, r=alexcrichton