Fix free logic

[jamesmunns]

The existing 0.10.0 free logic can be incorrect in certain conditions. This can lead to failing assertions due to incorrect preconditions.

I plan to add tests to this to ensure that there are no additional issues, but this should likely be merged ASAP and 0.10.0 should be yanked.

[jamesmunns]

This fixes two bugs in the 0.10.0 release.

1. The insertion logic in the prior version was incorrect, throwing false-positive assertions
2. Additionally, there were some cases when a freed allocation was at the start/end of the allocation region, but there was not room for a hole before/after the allocation, essentially leading to leaking of that memory

In order to test this, I've added a much more exhaustive test, which allocations and frees in a variety of different size, alignment, and free-order strategies.

[haraldh]

@phil-opp please release 0.10.1 with these fixes

[phil-opp]

Thanks for the ping and sorry for the delay! I yanked v0.10.0 on crates.io and I will review this PR as soon as possible. Does this PR supersede your PR at #63, or should both be merged?

[jamesmunns]

I think this change supercedes #63, though if you'd like me to merge in @haraldh's test case changes, I can!

@phil-opp if you'd like to add me as a maintainer for this crate and share crates-io permissions, I'm happy to help out.

Sorry again for the fire drill!

[phil-opp]

No worries, thanks to both of you for creating fixes so quickly!

@phil-opp if you'd like to add me as a maintainer for this crate and share crates-io permissions, I'm happy to help out.

That would be great! I just set up a team for maintaining this crate and sent you an invite. You should then have crates.io access too.

[jamesmunns]

Got it! Let me know if you'd like me to merge this + release, otherwise I'll hold on for your review!

[phil-opp]

I didn't have time for an in-depth review, but the changes look all reasonable. Thanks again and sorry for the delay!

Feel free to merge and release this yourself, then we see if I set up the permissions correctly. For creating the releases of this crate, I use the cargo-release tool, which will automatically bump the version number, create the release tags, and update the changelog headings. Just cargo release patch --execute should be enough.