Open Source Announcement: phased releases for Sparkle-based macOS apps

This post introduces a new capability for phased app updates, open-sourcing the `Progressive-Rollout-via-Sparkle` library. The library includes `PRGUpdateHelper` for randomized group management, `PRGGroupPercentageTransformer` for mapping groups to percentages, and `NSString+PRGHashing` for SHA1 hashing. It also details the integration with fastlane for distribution, including custom lanes for alpha, beta, and one-off builds, and an `update` lane for phased rollouts. The post highlights the use of this system in SourceTree 2.4 to manage disruptive changes and gather user feedback.