Create v1.0.0-rc.3 release

[SteveLasker]

Complete the v1.0.0-rc.3 release in prep for a 1.0.0 release

High-level deliverables as follows:

• [ ] Decide on main commit for release -
• [ ] Cut branch named v1.0.0-rc.3 based on agreed upon main commit
• [ ] Cut a tag named v1.0.0-rc.3
• [ ] Update README.md

~Can the maintainers please respond with a +1 comment once you are in favor of cutting this release?~

[SteveLasker]

Closing as we're releasing 1.0 (#98 )