I am not certain if this will improve performance,
but it seems having a .clone() without any need should be removed.
This was done with clippy, and manually reviewed:
```
cargo clippy --fix -- -A clippy::all -D clippy::redundant_clone
```
This has to re-introduce the `sink` pattern, because doing this purely
with iterators is awkward :( Maaaybe the event vector was a false start?
But, anyway, I like the current factoring more -- it sort-of obvious
that we do want to keep ws-attachment business in the parser, and that
we also don't want that to depend on the particular tree structure. I
think `shortcuts` module achieves that.
