Release 2.5.0

This is a targeted test to make sure we cover all the heuristic edge
cases in `erase_indices`, used by `drain` and other methods.

I found a failure from `cargo mutants` where we still passed tests after
`erase_indices_sweep` was replaced with an empty body. I was concerned
because that function contains `unsafe` code, so we *really* need it
tested. It turns out that we do *sometimes* hit that in `quickcheck`
tests, but might miss that if we're randomly unlucky, so this PR adds a
new test that will hit all the edge cases every time.

Test the various heuristics of `erase_indices`

Derive `Clone` for `{map,set}::IntoIter`

docs: Improve doc formatting with backticks

It did already panic as expected, but with a confusing message if the
`to` index was out of bounds. Now we have a direct bounds check for that
at the start, just as there already was for the `from` index.

Add an explicit bounds check in `move_index`

Use `hashbrown::HashTable` instead of `RawTable`

Release 2.6.0