wither-v0.9.0

Now that Model::sync index management is back, we are finally ready to release an official 0.9.0. All of the changes released so far as part of the various 0.9.0-alpha.* releases are included as part of this release. Big shoutout to @simoneromano96 for all of their hard work on the updates to Model::sync, thank you!

added

• I am happy to announce that index management via Model::sync is back! This has taken much longer than intended, but it is finally back. It also has a few improvements where index options are diffed in order to ensure that subtle updates to an index are observed and indexes are re-created as needed. This closes #51.
• Added the delete_many method.