Release 3.0.0-rc

3.0.0-rc.1 is the first release candidate for Quantum 3.0.0.

This RC is for final validation of breaking changes, response-return contracts, and template/generator consistency before stable release.

Upgrade guide:
https://github.com/softberg/quantum-php-docs/blob/master/v3.0/upgrade-guide.md

Please report only release-blocking issues for this RC window.