Start of 2.8.0 "Gutsy Gibson"

Hot on the heels of the release of 0.27.4, the `playground` now contains the code for what will become 2.8.0. There's nothing new, it's just 0.27.4 with the multiprocess bits merged in. I bumped the version to 2.8.0 instead of 0.28.0 (or 0.27.5) because I want to switch to strict [semantic versioning](http://semver.org), not because there are actually any major changes.