Get rid of `locate()` in markdown handling

This function was unfortunate for several reasons:

- It used `unsafe` because it wanted to tell whether a string came from
  the same *allocation* as another, not just whether it was a textual
  match.
- It recalculated spans even though they were already available from
  pulldown
- It sometimes *failed* to calculate the span, which meant it was always
  possible for the span to be `None`, even though in practice that
  should never happen.

This commit has several cleanups:

- Make the span required
- Pass through the span from pulldown in the `HeadingLinks` and
  `Footnotes` iterators
- Only add iterator bounds on the `impl Iterator`, not on `new` and the
  struct itself.

0 files changed, 0 insertions, 0 deletions