Annotate snippets 0.10.0

[Muscraft]

This PR updates the CHANGELOG.md in preparation for 0.10.0, as well as bumps the version number to 0.10.0. I have tried my best to capture what changes were made and added a note saying that annotate-snippets is in the middle of a rewrite and that there could be more breaking changes in future releases.

Note: I have not created a tag for 0.10.0 (I am unsure how to create one or if I have permission to do so), so the updated links will not work until one is created.

Note: This release will help unblock work on a diagnostic system for cargo. It will allow work to be done while this crate is being evolved.

[Muscraft]

I was able to create the 0.10.0 tag, but I do not have the ability to publish the new version on crates.io. @zbraniecki can you do this? If not, can you add me as an owner or someone who can publish?

[Muscraft]

@zbraniecki, I am just checking to see if you could give me the ability to publish sometime in the next few days. Work on cargo's diagnostic system is blocked as it requires a few things from 0.10.0. As well, giving me the ability to publish would be helpful as I experiment with how annotate-snippets should look and cargo's (and hopefully rustc's) usage of it.