Steer docs to `utf8_chunks` and `Iterator::take` - Adds `limit` as an alias of `take` (as this is [what Java calls this operation](https://docs.oracle.com/javase/8/docs/api/java/util/stream/Stream.html#limit-long-)); - Says that [`Utf8Chunks`](https://doc.rust-lang.org/std/str/struct.Utf8Chunks.html) comes from [`[u8]::utf8_chunks`](https://doc.rust-lang.org/std/primitive.slice.html#method.utf8_chunks). ``@rustbot`` label +A-docs